(for example, never running for office if you dont have a role etc)I have two solutions to that. First the detective can be downgraded so that he can no longer spot the exact role that the player has. He'll only is able to see if the person is pro-townie or a criminal. Thus the non role townies are safe to run for office again (and so is the Godfather). I'm implementing this rule in the game that I'm currently promoting.
Alternatively, we can issue a new rule stating that people in power can not be approached by the detective (or anyone else) as long as their bodyguards are alive. The detective is still free from examining the candidates during day one so he can still attempt to look up the prospecting mayor/pardoner. That way it's easier for the mafia to sneak in one of their members while they're still at some risk.