hummm maybe a leash is the key? every time he chases a cat i yell no stop don't do that and he just ignores me and keeps on running. lol
I got the best advice from a friend who has a dog trained to do things most people could never get their dog to do. You tell this dog to get a rope, it gets a rope, you tell it to get a ball, it gets a ball. He said "If you're trying to stop the dog from doing something, you have to tell it in its own language. Youre the packleader, so BE the packleader."
So when my dogs do something I don't want them to do, I growl at them. And I mean seriously growl, like a dog would, lips pulled back, sounding like I could bite a postman. If they're far away, I get their attention by yelling their name in a growly manner. Deepen your tone and add gravel to your voice. It changed the way my dogs responded almost overnight. If you can catch them doing something wrong, grab them by the scruff and hold them, growl and say NO in that deep voice.
That one change also helped me realize something else. I have one dog that whines and whimpers constantly when she's around me, and what I perceived as a sycophantic and grovelling nature was annoying. I was raised to believe that dogs, like babies, hear better in higher ranges, so I talk to them sometimes in that high pitched singsong babytalk voice. One day I realized she wasn't whining and whimpering... she was talking to me in her happy voice... the one she'd learned from me. She wasn't grovelling, she was communicating her joy. She was smart enough to use my language before I figured out how to use hers.
The growling will help to alter their behavior, but you still have to worry about how they behave when you're not around, and the only way to do that is to train them to believe that chickens are part of the pack and need their protection. Take them into the pens with you, on a leash at first, let them see you handling the flock, growl if they assume a stance or get that hunting look on their face. When they're no longer jumping or lunging, let them off the leash and keep watching them. It'll take a while, but the more they see you treating the chickens as part of your pack, the more they will be driven to treat them well as an extension of you.