Once Zeke got comfortable with his feline sister, he decided to assert his dominance and would attack her hind end anytime she walked by him. As you have, we got very frustrated and wondered what to do. We got extremely lucky and the first aversion training we tried with him has worked. We got several water bottles from the travel sized health and beauty section at Wal-Mart and placed them strategically around our house so that one was never out of hand's reach. The first time that Zeke went after Sasha's hind end we sprayed him (make sure you set the sprayer so that it sprays out a line and not a fine mist) on his hind end and firmly said "NO CAT!". When he looked back again to see where the spray was coming from, we held up the bottle and said again "NO CAT". It only took getting sprayed twice before he stopped running after her hind end. Now if he looks like he's going to take after her all we have to do is say "NO CAT" and he settles down. This has also been an excellent way to stop him from doing other things we don't want him to do like zealously licking any patch of salty skin to be found. I don't mind it so much, but my balding (and very sensitive about balding) Dad got very upset when he took off his hat and Zeke went straight for his shiny (and salty) bald head!
