He gets lots o' stuff to clean, and I don't have to deal with it the last week I'm here. As codependency goes, however, I've seen worse. No one was even injured or incarcerated.

No suggestions for an overinvolved parent though; my working theory is "leave the country and get married". I tend to agree with Mike though: Subtlety rarely works in these situations, and it's already failed here, so getting the key back is probably your only option. Unless you're ready to ask him to move over it your roommate has to ask HIMSELF whether he'd rather have dad coming to clean all the time, or confront him over the key. Oh, and before you urge THAT confrontation, best make sure the roommate will be cleaning up when dad isn't.

Good luck with it, anyway. *hugs*