Sounds like you are describing my German Shepherd.Its gonna take a lot of dedicated training. I know for me, my very high prey driven husky mix isn't worth it. She's crafty and will behave around chickens as long as your within sight... but the minute she thinks you can't see her, she'll grab a chicken. My ex had free range around his place and she wouldn't even look at them if you were standing right there. One could walk up to her even, but the there was one time we were all in the barn and she grabbed one by the head. Thankfully I caught on before she did any damage, but now that I've got chicks, I'm not even giving her the opportunity to be near them. I'm hoping my terrier will do better.