While tax compliance can be modelled as a form of self-insurance against sanctions for tax evasion, also forms of self-protection are actually used by firms. The latter involve the cooperation of gatekeepers (employees, consultants, tax preparers) who can manipulate tax reports and in general have an increasing role in taxation and regulation. From the point of view of the public interest, while burdening gatekeepers with legal liability for misconducts that benefit those who resort to their services actually discourages wrongdoings, an alienation effect can also arise. That is, the gatekeeper might become more interested in covering up the illegal behavior and in cooperating with the perpetrator. Such perverse effects are difficult to detect and to measure. This problem will be studied by building upon the classical Allingham and Sandmo (1972) model and by providing a more detailed description of the concealment costs than that available in the literature, which often simply makes assumptions about their existence and their functional form. The relationship between a risk neutral firm owner aiming at evading taxes and a risk averse gatekeeper will bedescribed through a simple principal-agent framework.The purpose is that of studying the role of legal rules pertaining to liability for tax evasion in shaping the parties choices, since concealment costs vary according to whether the risk neutral principal or the risk averse agent are held responsible when tax evasion is detected.