Ive done the smack on the bum thing a bit lately too
Usually when she hurts her sister - then I tell her she has to go and sit on the tiles (the most un-fun place in the house!) and she says "no" or screams, or hits/scratches/bites me - so I get grumpy and give her a little smack!

The other thing at the moment is yelling - I yell from the kitchen "stop yelling!"