I would get a chain lock, if nothing else; that way he can't come in if you're home, even if he has the key. That's really too bad, I'd write a letter to management, reiterating he's supposed to call first! (Of course, if you don't answer the phone then he'll think you're not there and come in to fix whatever, since he doesn't want to be in your way in the first place). Maybe insist on making an appointment time?