Our trainer said not to let a dog "practice" bad behavior. Therefor make sure the dog cannot act out the bad behavior. Then put the dog in a well controlled test situation and start aversion training. We created a short run with temporary fencing for the chickens and when the dog came near them I squirted her with a water bottle. I did this over and over for more than two weeks. Eventually she lost interest, at which point she got a treat for good behavior. I believe this worked with our dog, since she wasn't actually trying to kill the chickens, she saw them as toys. It is now a year later and we are able to let our dog and chickens out at the same time, but usually one of us is out with them. We don't leave them out together all day unless we are out there too. Our dog still likes to run after a sole chicken that gets out, especially the roosters. And she is a quick plucker!!! So we rather not take chances. Good luck!!