[She bites her lip thoughtfully for a moment.]

I'm not sure what would happen if someone cast it while he was inside. I mean, it wouldn't eject him from the house or anything... I would say there's a good chance it would just fail - the spell I adapted this one from would. But magic can be a little tricky... I guess there's a chance it could either seal him in or stop him from coming back if he left. That's... probably not something we want to find out the hard way, though.