Sosman, J.
Modem Continental/Obayashi (Modem) sought judicial review of a decision by the Massachusetts Commission Against Discrimination (MCAD) finding Modem liable for sex discrimination when Modern failed to protect one of its employees from harassment by employees of one of Modem’s subcontractors. A judge in the Superior Court affirmed the MCAD’s decision, and Modem appealed. We transferred the case to this court on our own motion. Although we reject Modem’s contention that an employer can never be liable for sexual harassment perpetrated by outside third parties, we agree that, on this record, Modern satisfied its obligation to its employee by making reasonable efforts to remedy the harassing conduct. The MCAD’s decision to the contrary is not supported by substantial evidence, and instead reflects the imposition of an erroneous standard higher than reasonableness. We therefore reverse the judgment.2
1. Facts and procedural background. On January 18, 1994, Whatleigh Edmands, a female employee of Modern, filed a complaint with the MCAD charging Modem with sex discrimination based on sexual harassment. She subsequently amended her complaint to add Mohawk Construction (Mohawk), one of Modem’s subcontractors, as a respondent, but ultimately settled her claim against Mohawk. She amended her complaint again to add a claim that she was constructively discharged from Modem as a result of a hostile work environment. The investigating commissioner found probable cause to support the claim of sexual harassment, but no probable cause to support the claim of constructive discharge. The matter went forward to a public hearing solely on the sexual harassment claim. The hearing commissioner’s findings on that claim are as follows, supplemented by uncontested details from the record.
[98]*98Modem was the successful bidder on a public works project to prepare the eastern approach to the Ted Williams Tunnel, a portion of the Central Artery/Tunnel project (the so-called “Big Dig”). Modem subcontracted the iron work on the project to Mohawk. As a condition of its contract, Modem and all of its subcontractors entered into a project labor agreement with the construction trades unions, which required, inter alla, that all craft employees (including foremen) be union members, that all such employees be hired through exclusive union hiring halls, and that workers not be disciplined or terminated except for “just cause.”
Whatleigh Edmands, an apprentice carpenter, was hired by Modem through the carpenters’ union in October, 1993. She worked with four or five other caipenters on a crew supervised by foreman Charles Cofield. Numerous other tradespeople were on the site, including ironworkers employed by Mohawk. On November 3, 1993, Edmands was using one of the portable toilet facilities on the site when she heard scratching noises outside. Looking up, she saw someone peering through an air vent near the roof. The peeper was wearing a brown hard hat of a type worn exclusively by the ironworkers. When Edmands tried to exit, she found herself unable to open the door, as a tie wire had been fastened around the toilet enclosure.3 She screamed, and someone cut the tie wire to let her out. As she came outside, she saw approximately twelve men in the area. She yelled at them, demanding to know who had spied on her and tied her in the portable toilet facility. None of them responded.
Later that day, Edmands informed Cofield of the incident, and Cofield assured her that he would “take care of this.” The following day, Richard Ell, the steward for the carpenters’ union, came to see Edmands about the incident, and, the next day, returned to see Edmands with Jay Kennedy, the steward for the ironworkers’ union. Ell informed Edmands that one of the ironworkers, Joe Roselli, had admitted responsibility for tie wiring Edmands into the toilet facility. Ell asked Edmands if she wanted to have Roselli apologize in person, suggesting that seeing him might enable her to identify him as the person who had [99]*99peered in through the vent. Although Edmands said that she did not wish to speak to Roselli, Roselli was brought over and made his apologies to her. He admitted that he was the one who had fastened the tie wire, but claimed it was a prank that he intended to play on another ironworker, and that he had thought someone else was using the toilet facility at the time.4 Roselli denied that he had looked through the vent. After hearing from Roselli, Ell asked Edmands if she could identify Roselli as the person who had peered in through the vent. She could not. At the hearing, Edmands testified that Roselli was not the peeper.
On November 8, five days after the incident, Edmands and Ell met with Modem’s project manager, John McNamara. McNamara indicated that he would speak with the ironworkers’ business agent to have Roselli removed from the site. McNamara also suggested that Edmands view the videotapes of the work site to see if those tapes would help her identify the person who had peered in through the vent. Thereafter, McNamara contacted Mohawk’s president, requesting that Mohawk investigate the matter. He also asked Mohawk to transfer Roselli off the job site, but Mohawk refused to remove him or to discipline him.
On November 10, Edmands noticed that the portable toilet facility had been defaced with graffiti, consisting of the word “HERS” written above a drawing of an eye and, below the eye, a cmde caricature of female genitalia. Edmands understood that the graffiti was directed at her, and that it referred to the prior week’s incident. She encountered Cofield and Ell a short time later; Cofield again promised to “take care of this,” and the graffiti was removed.
Following up on McNamara’s suggestion about the videotapes, Edmands reviewed the tapes on November 15. However, the camera angle was such that, despite reviewing the tapes twice, Edmands still could not make any identification. Two days later, George Coblyn, Modem’s equal employment opportunity officer, spoke with Edmands and asked her to give him a written statement concerning both the original peeping [100]*100and tie wiring incident and the graffiti incident. She provided him with such a statement two weeks later. That statement contained no identification of either the perpetrators or of any potential witnesses. Coblyn also contacted employees and officials at Mohawk. They refused to provide him with any information concerning the identity of the perpetrator of either the peeping incident or the subsequent graffiti.
On November 23, Coblyn gave a brief presentation on the subject of sexual harassment, including a warning that sexual harassment would not be tolerated at the site, at a regular gathering of workers, managers, and union representatives referred to as “tool box talks.”5 However, very few persons attended that particular tool box talk.6
Without Edmands’s knowledge, her union initiated a grievance with respect to these incidents, and on December 7, she was called to attend a step one grievance meeting. In addition to various officials from Modem, the meeting was attended by the ironworkers’ union business agent, Sonny Oliver; the ironworkers’ steward, Jay Kennedy; and Roselli. Oliver, on [101]*101behalf of the ironworkers, dominated the meeting.7 Oliver denied that anyone had peered into the toilet facility while Edmands was using it. He also insisted that the facility had been shut with a tie wire in order to prepare for its removal by a crane (a version contrary to Roselli’s prior admission that he had tie wired the facility as a prank). McNamara repeated his request that Roselli be transferred off the project. At that, the ironworkers threatened to strike if Roselli were removed.
Oliver also raised issues concerning the cleanliness of the toilet facilities. There ensued some discussion concerning the security and cleaning of the facilities, resulting in a “general agreement” that certain of the toilets would be designated for exclusive use by female workers (instead of being entirely unisex, as they had been until that point), and that they would be separated from the men’s toilets, set off by fencing, and secured with padlocks. However, from the date of the original November 3 incident onward, Edmands had opted to use the bathroom facilities at a building one-quarter mile away, and she continued to do so even after these additional security measures were later instituted.
Although unable to convince Mohawk to remove Roselli, and unable to uncover the identity of any other perpetrator, McNamara revised the work schedule at the site so that iron work would be done at a different location (some 500 to 700 yards from where Edmands worked) and on a different shift. Although Edmands still would encounter Roselli (and other ironworkers) at shift changes, she would not be working with ironworkers in the immediate vicinity.
McNamara had been skeptical of the efficacy of padlocking the newly-designated female toilet facilities, but he carried through with the ordering of separate facilities, the placement of signage, the installation of padlocks, and the issuance of padlock keys to female employees.8 Within a few weeks, the padlocks [102]*102on the women’s toilets disappeared. Some fencing was erected, but quickly fell down or was removed. And, instead of placing the facilities in separate locations, the women’s toilets were frequently placed side by side next to the men’s toilets.
In February, 1994, a step two grievance meeting was held, attended by Edmands, officials from the carpenters’ union, and officials from Modem. Although she was not using the facilities in any event, Edmands complained that Modem had failed to carry through on its agreement to separate, fence, and lock the women’s portable toilets. Modem took the position that fencing had been a suggestion at the prior meeting, but not an agreed item. At the step two meeting, it was agreed that the female facilities would be kept separate, surrounded by fencing, and locked. In addition, a security monitor would be hired, assigned to report on any further problems, including any incidents of sexual harassment or graffiti.9 Finally, Modem confirmed that Roselli had been moved to a different location and different shift. Based on the results of the step two grievance meeting, the carpenters’ union, with Edmands’s agreement, decided not to take the matter to arbitration.
On March 21, 1994, as Edmands was entering her work trailer, she encountered her foreman, Cofield, erasing graffiti. Edmands did not see the graffiti, but Cofield informed her that it had consisted of depictions of male and female genitals.
By late March or early April, 1994, the task that ironworkers had been assigned at a different location and shift was completed. As a result, Roselli and the ironworkers returned to the day shift, working in a location near Edmands.10 Shortly thereafter, the monitor hired to patrol the toilet facilities discovered some graffiti in the men’s toilet facilities that [103]*103referred to Edmands in vulgar terms, and brought it to Coblyn’s attention. (Edmands did not see it.) Coblyn in turn reported this new outbreak of graffiti to McNamara, who instructed him to draft a memorandum, to be distributed to all workers at the site over McNamara’s signature, responding to the incident. Thereafter, Coblyn supplied McNamara with the requested draft memorandum.11 Instead of distributing the notice drafted by Coblyn, McNamara drafted his own notice, which focused on the specific problem of vulgar graffiti.12 That notice was distributed to all workers with their paychecks.
Later that month, Edmands told Coblyn that she was tired of working in an environment that made her “nervous and scared,” where people were “so angry at [her] for just wanting to work.” She also contacted her union and asked to be transferred to a different job site. Coblyn suggested that she could be transferred [104]*104to work in a facility referred to as “the mill,” which was part of the same project but at a removed location. Although some workers considered the mill a better assignment (as it was a more comfortable indoor site with more amenities), Edmands considered the work at the mill to be less challenging and a less valuable experience than work in the field. She nevertheless agreed to the transfer.
At the mill, Edmands’s foreman, Steve Pema, remarked that, in his view, women working outside the home were adversely affecting the economy. He then clarified that he was referring to women of his own age (i.e., of an age significantly older than Edmands). When Edmands reported these remarks to an equal employment opportunity officer, the officer told her that Pema’s inappropriate comments used to be worse. Edmands quit her job at Modem in May, 1994, and went to work for a technology company as a software engineer.
The hearing commissioner found that the incidents were sexual in nature or, even if not explicitly sexual in nature, that they had been directed at Edmands because of her sex; that their cumulative effect was sufficiently severe that it impacted Edmands’s working environment and triggered a duty on the part of Modem to take action; and that Modem’s response to these incidents of harassment was inadequate. He therefore found Modem liable for sex discrimination, awarded Edmands $50,000 in damages for emotional distress, and ordered Modem to submit and implement a plan acceptable to the MCAD to train all of Modem’s Massachusetts employees concerning “the legal requirements of nondiscrimination in the workplace.” Modem appealed to the full commission, which affirmed the hearing commissioner’s decision in all respects and awarded Edmands attorney’s fees and costs.
2. Discussion, a. Employer’s liability for harassing acts committed by third parties. Modem contends that, as a matter of law, it cannot be held liable for the conduct of independent third parties over whom it did not have control.13 The only known perpetrators of the harassing acts at the project site were [105]*105ironworkers employed by Mohawk; there was no evidence of any such acts committed by employees or agents of Modem. Modem’s argument relies on the literal wording of the statutory prohibition against sexual harassment: it is an unlawful practice “[f]or an employer, personally or through its agents, to sexually harass any employee” (emphasis added). G. L. c. 151B, § 4 (16A). Mohawk was an independent subcontractor, and Mohawk’s offending employees were not the “agents” of Modem.
However, in addition to the prohibition set forth in § 4 (16A), Modem is also prohibited from discriminating against its own employees on the basis of sex (including discrimination with respect to the “conditions” of employment), G. L. c. 15IB, § 4 (1); and discrimination on the basis of sex includes sexual harassment, G. L. c. 151B, § 1 (18). An employer who passively tolerates the creation of a hostile working environment implicitly ratifies the perpetrator’s misconduct and thereby encourages the perpetrator to persist in such misconduct, whatever the employer’s precise legal relationship to the perpetrator. Moreover, acquiescence on the part of the employer effectively communicates to the victim of harassment that her employer does not care about the hostile environment in which she must work, a message that can only operate to exacerbate the adverse effects of that hostile environment. In this context, an employer who is not part of the solution inevitably becomes part of the problem. Bearing in mind that the statute “shall be construed liberally for the accomplishment of [its] purposes,” G. L. c. 151B, § 9, we decline to read it in a manner that would absolve an employer of all responsibility for a hostile work environment merely because that hostile work environment is attributable to persons who are not the employer’s own employees or agents.
[106]*106The MCAD guidelines on the subject of sexual harassment provide that an employer may, in some circumstances, be held liable for sexual harassment perpetrated by persons who are not employees of the employer. Massachusetts Commission Against Discrimination Guidelines: Sexual Harassment in the Workplace § IDLC (2002) (MCAD Guidelines). Specifically, liability may be imposed where the employer knew or should have known of the harassing conduct but “failed to take prompt, effective and reasonable remedial action.” Id. The MCAD Guidelines recognize that an employer may have less control over perpetrators who are not its own employees, and the factor of control is to be taken into consideration in determining whether the employer should be held liable: “The primary difference between employer liability for harassment perpetrated by co-workers and harassment committed by non-employees lies in the ability of the employer to control the conduct of the non-employees. The greater the employer’s ability to control the non-employee’s conduct, the more likely it will be found liable for that person’s unlawful harassment.” Id. Where the Legislature has expressly delegated to the MCAD the task of “formulat[ing] policies to effectuate the purposes” of G. L. c. 151B and given it authority to “adopt, promulgate, amend, and rescind rules and regulations” to implement the statute, G. L. c. 151B, §§ 2, 3 (5), we accord substantial deference to the MCAD’s interpretive guidelines. See Dahill v. Police Dep’t of Boston, 434 Mass. 233, 239 (2001), and cases cited. Here, the MCAD’s interpretation is a reasonable one, whereas the interpretation proposed by Modem would seriously undermine the objective of eliminating sexual harassment in the workplace.
The MCAD’s interpretation is also consistent with a considerable body of Federal precedent interpreting comparable provisions of Title VII of the Civil Rights Act of 1964.14 Regulations of the Equal Employment Opportunity Commission (EEOC) [107]*107interpreting Title VII recognize that an employer may be liable for sexual harassment perpetrated by third parties: “An employer may also be responsible for the acts of non-employees, with respect to sexual harassment of employees in the workplace, where the employer (or its agents or supervisory employees) knows or should have known of the conduct and fails to take immediate and appropriate corrective action. In reviewing these cases the Commission will consider the extent of the employer’s control and any other legal responsibility which the employer may have with respect to the conduct of such non-employees.” 29 C.F.R. § 1604.11(e) (2004). Although the EEOC’s position is not entitled to any particular deference, see Cuddyer v. Stop & Shop Supermarket Co., 434 Mass. 521, 536 & n.18 (2001), and cases cited, the EEOC regulation here is consistent with the interpretation adopted by the MCAD. Both the MCAD Guidelines and the EEOC’s regulations articulate the position that, once the employer knows or should know of the harassment being perpetrated by others, the employer is under an obligation to take reasonable steps to cure that harassment, giving consideration to the extent of the employer’s ability to control the conduct of the third-party perpetrator.
Numerous Federal courts, informed by the EEOC regulations on this issue, have held that an employer may be liable for sexual harassment perpetrated by persons who are not employees or agents of the employer.15 See Watson v. Blue Circle, Inc., 324 F.3d 1252, 1258 n.2 (11th Cir. 2003); Little v. Windermere Relocation, Inc., 301 F.3d 958, 968 (9th Cir. 2002); Turnbull v. Topeka State Hosp., 255 F.3d 1238, 1244 (10th Cir. 2001); Lockard v. Pizza Hut, Inc., 162 F.3d 1062, 1073-1074 (10th Cir. 1998); Rodriguez-Hernandez v. Miranda-Velez, 132 F.3d 848, [108]*108854 (1st Cir. 1998); Crist v. Focus Homes, Inc., 122 F.3d 1107, 1111-1112 (8th Cir. 1997); Folkerson v. Circus Circus Enters., Inc., 107 F.3d 754, 756 (9th Cir. 1997).16
We thus conclude, consistent with the MCAD Guidelines, the EEOC regulations interpreting Title VII, and the vast body of precedent applying those regulations, that an employer may be held liable for failing to respond reasonably to acts of sexual harassment of which it is aware or reasonably should be aware, even though the harassing acts are perpetrated by someone who is not an agent or employee of the employer.
b. Standard for imposing liability for harassment by a third party. Under the MCAD Guidelines, and under comparable Federal precedent applying the EEOC regulations, an employer is not held strictly liable for sexual harassment perpetrated by nonemployees. The standard is one of reasonableness: did the employer take “prompt, effective and reasonable remedial action,” MCAD Guidelines, supra, or “immediate and appropriate corrective action,” 29 C.F.R. § 1604.11(e), once it realized or should have realized that one of its employees was being victimized by a third party’s harassment? The standard imposed has been referred to as a “negligence” standard. See Turnbull v. Topeka State Hosp., supra; Lockard v. Pizza Hut, Inc., supra at 1074; Mart v. Dr Pepper Co., 923 F. Supp. 1380, 1388 (D. Kan. 1996); Woods-Pirozzi v. Nabisco Foods, 290 N.J. Super. 252, 272 (App. Div. 1996). It imposes a duty “to take prompt action reasonably calculated to end the harassment and [109]*109reasonably likely to prevent the conduct from recurring.” Berry v. Delta Airlines, Inc., 260 F.3d 803, 813 (7th Cir. 2001).
Under this standard, the fact that an employer’s efforts do not actually succeed in stopping or preventing the harassment is not determinative. “We are not to focus solely upon whether the remedial activity ultimately succeeded, but instead should determine whether the employer’s total response was reasonable under the circumstances as then existed.” Id. at 811, citing McKenzie v. Illinois Dept. of Transp., 92 F.3d 473, 480 (7th Cir. 1996). Although the “promptness and effectiveness” of the employer’s response are key considerations, “[i]t is not always possible for an employer to completely eliminate offensive behavior, and thus the effectiveness inquiry looks not to whether offensive behavior actually ceased but to whether the ‘remedial and preventative • action was reasonably calculated to end the harassment.’ ” Turnbull v. Topeka State Hosp., supra at 1245, quoting Adler v. Wal-Mart Stores, Inc., 144 F.3d 664, 676 (10th Cir. 1998).
Nor is an employer required to take what would, with hindsight, be considered better or more effective measures. “[T]he inquiry is not whether [the employer’s] response was the best course of action possible, but rather whether it was appropriate in light of all the circumstances” (emphasis in original). Crist v. Focus Homes, Inc., supra at 1112 n.5. Thus, a plaintiff does not establish an employer’s liability merely by showing that the employer “could have done more.” Berry v. Delta Airlines, Inc., supra at 813. Rather, the plaintiff must show “that the steps that [the employer] actually took were not reasonably likely to prevent the harassment from recurring.” Id.
In the same vein, the employer is not required to respond with the precise remedy that the harassment victim wishes or asks for — the victim does not have a right to “dictate the remedy the employer chooses to stop the harassment.” Hallberg vs. Eat’n Park, U.S. Dist. Ct., No. Civ. A. 94-1888 (W.D. Pa. Feb. 28, 1996). In that case, for example, the plaintiff, a waitress who had been sexually harassed by a customer, was of the view that the offending customer should have been banned from the premises immediately, whereas the employer’s remedial action had consisted of warning the customer that any future complaint [110]*110of similar misconduct would result in his being barred from the restaurant. Id. Although the employer’s response was not as forceful as what the employee wished, it satisfied the employer’s obligation, as it was “reasonably calculated to stop the harassment.” Id., quoting Saxton v. AT&T Co., 10 F.3d 526, 536 (7th Cir. 1993). Similarly, in Gliatta v. Tectum Inc., 211 F. Supp. 2d 992, 1002 (S.D. Ohio 2002), the employee complained that her supervisor, who had been present when a nonemployee made explicit sexual comments, failed to say anything to the perpetrator on the spot. However, her employer took action a few days later, sending a letter to the perpetrator forbidding him from attending future events and thereby ensuring that he would have no further contact with the plaintiff. Id. Notwithstanding the employee’s understandable disappointment that her supervisor had not reacted immediately to the inappropriate remarks, the employer’s response satisfied the standard of “appropriate action.” Id. Thus, the mere fact that the victim is not satisfied with the employer’s response does not suffice to render that response unreasonable.
c. Analysis of Modem’s response to third-party harassment of the plaintiff. Applying the above standards to the remedial steps taken by Modem, we conclude that, as a matter of law, they satisfied Modem’s obligation to take prompt action that was reasonably calculated to end the harassment being perpetrated on Edmands. The MCAD’s decision imposing liability on Modem erroneously held Modem to the equivalent of strict liability because its remedial actions were not entirely successful and because, in the MCAD’s and the plaintiff’s view, Modem could have taken other or additional steps faster than it did. As discussed above, criticism in the form of alternative or additional remedies that might have been pursued do not suffice to render Modem’s remedial steps unreasonable. Instead, we must focus on the remedial steps Modem did undertake, and whether, in all the surrounding circumstances, those measures were reasonably calculated to end and deter any further harassment. Where, as here, the employer did take action in an attempt to remedy the harassment, the reasonableness of that remedial action can be determined as a matter of law. See, e.g., Berry v. Delta Airlines, Inc., supra at 813-814 (summary judg[111]*111ment for employer on ground that corrective actions were “reasonable and adequate under the circumstances,” even though employer “doubtless could have done more”); Gliatta v. Tectum Inc., supra (summary judgment for employer that “took appropriate action”); Mart v. Dr Pepper Co., supra at 1388 (summary judgment for employer that “took prompt, adequate and effective action to remedy the situation”); Hallberg vs. Eat’n Park, supra (summary judgment for employer that “took prompt action designed to stop the harassment”). See also Folkerson v. Circus Circus Enters., Inc., 107 F.2d 754, 756 (9th Cir. 1997).17 If Modem took such reasonable steps, it cannot be held liable.
Within two days of the initial incident, Edmands’s foreman had succeeded in identifying one of the perpetrators — Roselli, the ironworker who had fastened the tie wire around the toilet facility — and in obtaining his apology. Thereafter, Modem’s project manager asked both Mohawk and the ironworkers union to remove Roselli from the site. When that request was refused, Modem made arrangements to separate Roselli (and the other ironworkers) from Edmands for a period of at least several months, relocating his work and changing his shift. There can be no dispute that these methods were successful with respect to Roselli — following the original November 3, 1993, incident [112]*112up through Edmands’s resignation the following May (a period of approximately seven months), there is no evidence that Roselli ever engaged in further harassment of Edmands (or of any other woman on the project site). That Edmands would have preferred never to encounter Roselli again at all, or, in the hearing commissioner’s words, that Modem could have “taken more aggressive action to ensure [Edmands] would not encounter Roselli in the workplace,” is not the issue.18 The issue is whether Modem’s actions were reasonably calculated to prevent Roselli from further harassing Edmands. They were, and as to Roselli, they were in fact completely successful.
Roselli’s fellow perpetrators and, in particular, the ironworker who peered into the toilet facility while Edmands was inside, were never identified. The hearing commissioner faulted Modem for not having “thoroughly investigated” the original incident, suggesting that Modern should have “ spoke[n] to employees who were in the vicinity.” There is no dispute that Modem made efforts to uncover the identity of the various perpetrators, but those efforts were stymied by the fact that Edmands herself could not make any identification of the perpetrators (either from her recollection of the incident or from her [113]*113review of the videotapes),19 and that Mohawk, under apparent pressure from the ironworkers union, refused to investigate its own workers or supply information to Modem. Modem’s project manager asked Mohawk to investigate, but received no cooperation. Efforts by Coblyn to speak with Mohawk employees and officials were also rebuffed.20 Speculation that additional efforts to speak with unidentified “employees who were in the vicinity” might have yielded further information as to additional perpetrators does not operate to undermine the reasonableness of the investigative efforts that Modem made.
Moreover, the issue is not whether additional perpetrators could have been identified so that they could be dealt with individually. The issue is whether, lacking such identification when its investigation was blocked by the intransigence of Mohawk and the ironworkers’ union, Modem made reasonable efforts to prevent further harassment. It did so. Modern’s displeasure over and desire to remove the perpetrators of the tie wire and peeping incident was made known to Mohawk officials, to the ironworkers’ union officials, and to Roselli. In addition, the relocation and rescheduling of the Mohawk work had the effect of removing all of the ironworkers — whether they had participated in the harassment or not — from Edmands’s immediate work area, thus ensuring that her contact with the unidentified perpetrators would be minimized for a period of some months. Other than isolated incidents of graffiti (discussed infra), there was no form of sexual harassment perpetrated thereafter.21
The hearing commissioner also criticized Modem for making [114]*114only “limited efforts” to provide security for the women’s toilet facilities — e.g., the belated installation of fencing.22 However, the undisputed fact is that a variety of security precautions were taken, culminating ultimately in the assignment of a monitor to address any and all issues pertaining to the toilet facilities. That the hearing commissioner thought that these measures should have been implemented sooner or more aggressively does not undermine the reasonableness of Modem’s response. In fact, after the sole incident involving Edmands on November 3, 1993, there was no evidence that any other female was accosted, spied on, locked in, or otherwise harassed while using the women’s toilet facilities. Modem’s actions with respect to those facilities were apparently adequate. And, as to Edmands herself, she continued to use other toilet facilities, even after Modem implemented every security measure suggested. The presence or absence of any particular measure, or the timing of its implementation, was of no practical consequence to Edmands.
The hearing commissioner also found inadequate Modem’s steps with respect to three incidents of graffiti at the site, one such incident occurring on November 10, 1993; the next on March 21, 1994; and the last in early April, 1994. Although noting that “it is difficult for an employer to fully prevent graffiti, which is typically created both anonymously and surreptitiously,” he again opined that Modem somehow “could have more thoroughly investigated” these incidents of graffiti, without indicating what could realistically be done to identify [115]*115the anonymous and surreptitious perpetrator or perpetrators.23 He then criticized Modem’s response to this graffiti, expressing the view that Modem should have sent around Coblyn’s draft notice condemning “sexual harassment” instead of a warning notice focused “exclusively on graffiti in the workplace.” When the only form of sexual harassment that was then being perpetrated took the form of vulgar and sexually explicit graffiti, reasonable minds could differ about whether a warning notice complaining of “vulgar, obscene messages” and prohibiting “[offensive statements, whether written or verbal” anywhere on the work site would be more effective than a warning concerning “sexual harassment” in general. See notes 11 and 12, supra. If the purpose is to deter offensive graffiti, a notice prohibiting offensive graffiti is at least “reasonably calculated” to deter it. Indeed, from Coblyn’s proposed notice prohibiting “sexual harassment” or “any form of discrimination, coercion, intimi[d]ation or any manifestation that interfer[e]s” with another’s ability to perform the job, recipients would not necessarily appreciate that graffiti in places that the women workers would not see was a form of “sexual harassment” or “discrimination.” We see nothing unreasonable in Modem’s decision to send a pointed, as opposed to ambiguous, message on the subject of offensive graffiti.
Finally, the hearing commissioner criticized Modem for not engaging in more thorough and widespread educational efforts to instruct all workers on site about sexual harassment. Of course, on the record presented below, there was no evidence that sexual harassment was a widespread phenomenon among the multiple subcontractors and hundreds of tradespeople working at the site — Edmands’s problems stemmed exclusively from interactions with ironworkers, not from Modem employees or the employees of other subcontractors. Modem’s displeasure over the conduct of those ironworkers was made known to their [116]*116employer, Mohawk, and to their union. It was not unreasonable for Modem to expect that Mohawk (and the union) would communicate that displeasure to their own employees and undertake efforts at education. And, whatever the attendance figures at Modem’s own “tool box talks,” Coblyn gave repeated presentations on the subject of sexual harassment at those sessions. One can always conduct longer, more in-depth instruction to sensitize workers to the problem of sexual harassment, and one can always do more to ensure that every single worker attends such instructional sessions. That does not mean that Modern’s educational efforts, in combination with its other remedial efforts, were so insufficient as to signal that it “ratified or acquiesced in” the harassment perpetrated upon Edmands. Folkerson v. Circus Circus Enters., Inc., 107 F.3d 754, 756 (9th Cir. 1997).
The hearing commissioner’s decision also fails to take into account, or even to mention, the critical issue: whether Modem had the ability to “control” the persons perpetrating the harassment of Edmands. The MCAD Guidelines, the EEOC regulations, and the many cases applying those regulations recognize that the ability to “control” the third party perpetrator is a key factor in determining an employer’s liability for sexual harassment perpetrated by that third party. Where, for example, the perpetrator is a chent or customer, the employer often retains a considerable degree of control, as the employer may set the terms on which it is willing to do business with that chent or customer. See, e.g., Lockard v. Pizza Hut, Inc., 162 F.3d 1062, 1066 (10th Cir. 1998) (company manual recommended that managers deal with offending customers by “asking the customer to refrain from the conduct and if the customer persists, asking the customer to leave the restaurant”); Kudatzky vs. Galbreath Co., U.S. Dist. Ct., No. 96 Civ. 2693 (HB) (S.D.N.Y. Sept. 23, 1997).
Here, Modem was not deahng with a customer or a chent, but with a subcontractor’s employees. The hearing commissioner assumed that Modem could have “taken action against a subcontractor whose workers refused to comply with the [C]ommonwealth’s laws against workplace harassment.” However, the record does not contain a copy of Modem’s contract with Mo[117]*117hawk, and there is no basis for assuming that the single incident involving the portable toilet, for which Mohawk’s workers were responsible, or subsequent incidents of graffiti, which were probably (but not definitively) authored by Mohawk workers, would have allowed Modern to take any particular “action against” Mohawk. More importantly, making the extreme assumption that these infractions committed by Mohawk workers would have justified the termination of Modem’s contract with Mohawk (a conclusion that cannot be drawn on this record), even that drastic action would not have removed the offending ironworkers from the site. Pursuant to the project labor agreement (PLA), the ironworkers for the project had to be hired through the union’s hiring hall, and any successor to Mohawk would have been sent the same crew of ironworkers.
Similarly, Mohawk’s own ability to remove the perpetrators from the site was limited by the PLA. Under the PLA, a trade union worker, such as Roselli, could only be terminated for “just cause.” Roselli’s involvement in a single incident of harassment, for which he had apologized, followed by no further infraction, would not appear to be “just cause” justifying his termination. The union had made clear that it would pursue grievance and arbitration — and had threatened to strike — in the event that any form of discipline was imposed on Roselli. Effectively powerless to impose meaningful discipline on Roselli, Mohawk had even less power to discipline any additional suspected but unidentified perpetrators. The hearing commissioner’s assumption that Modem somehow had the ability to force Mohawk to take such steps is not supported on this record. Given that the employer’s ability to control the perpetrator is a critical factor for the imposition of liability, that ability to control must be demonstrated on the record, not assumed.
In short, lacking any evidence of the key element of “control” over the third-party perpetrators, we should be particularly wary of imposing liability on Modern for the misdeeds of Mohawk’s employees. There is nothing here to suggest that Modem encouraged the harassment perpetrated on Edmands, that it tacitly condoned it, or that it acquiesced in it. It took various measures to combat the harassment, which were, despite its lack of “control,” largely successful. That it could [118]*118not entirely stomp out occasional incidents of graffiti — the only form of harassment that persisted after the original incident — does not operate to make it liable.
We recognize the MCAD’s desire to take a strong stand to protect women working in the traditionally male-dominated construction trades. Its decision that Modem did not do enough in response to Edmands’s complaint, and its sweeping remedial order requiring Modem to undertake a multi-year discrimination and sexual harassment training program for all of its employees, reflects that laudable desire. However, the issue here is not whether Modem responded to Edmands’s complaint in ways that the MCAD would prefer, or whether its response was as emphatic and prompt as might be ideal. The issue is whether it took steps reasonably calculated to stop the harassment and prevent recurrence of the harassment, with the reasonableness of those steps considered in light of its practical ability to control the actual perpetrators. The obligation to make reasonable efforts cannot be transformed into an obligation to make maximum efforts. That Modem was not completely successful in eradicating all remaining vestiges of sexual harassment (i.e., occasional graffiti), and that one can envision additional steps that might have been taken (still with no guarantee of success), does not suffice to impose liability on Modem. Where the employer satisfied the threshold requirement of reasonableness, the MCAD cannot demand more.
Judgment reversed.