Is it ever justifiable to hit a girl?

I have a long history of domestic abuse, mostly because the girl I am involve with is in the wrong. I run a home-stay and most of the girls who live with me come from broken home in foreign countries. They are required to do housework, etc. I know that I shouldn't be violent towards them, but sometimes it's a guilty pleasure to their bare bottoms when they misbehave, break curfew and the rules I set out and make them say "thank you sir and please give me another". Is it justifiable? Is it weird? I know discipline is important, but what happens the adult is getting pleasure out of disciplining the youngsters?