I think you shouldn't go out of your way to make it hard. As has been said, write a proper contract in your POD, and let people bear the consequences if they break it.

Because occasionally, someone might want to break it with good reason. It is rare indeed, verily so, but it happens, as not every class is as well designed as one might wish for. No need to make things harder on people who know what they're doing.

Makeshifts last the longest.