Have you tried a rolled up newspaper? A good swat or two on the behind, along with verbal correction doesn't hurt them, but the sound startles them and diverts their attention from the behavior. This method helped to cure my lab, Chipper, of a multitude of sins when he was a puppy. I've also heard of filling a plastic jug with small rocks and throwing it near them (not on them - LOL) whenever they do something wrong. Good luck!