I think that the mistake most folks make in trying to train a dog to not kill, or to stop killing, a chicken is not having committed to training the dog already with just regular obedience training. When a dog is trained to be submissive to you and to react to your displeasure when they are engaging in bad behavior, training on livestock is 100% easier.
I read many stories on here about dogs who will pounce on a chicken right in front of their owner and kill the bird before they can stop it. A wise owner is always monitoring body language of their dogs in these circumstances and, with enough familiarity with their animal, can sense potential aggression towards other animals. A dog is, after all, merely a dog. They do doggy things and will do this first unless trained to check with the alpha for permission. I know that sounds like a bunch of hooey, but my dogs are always tuned in. They don't always do what I say but, when it comes to chickens or other livestock, they are very much aware that these are MINE. When I trained my pup, I always used the words "MY chickens" quite firmly, while forcing submissive posturing.
That was three years ago.....I can still walk out in my back yard and stand near the dogs and say, "MY chickens!!!" and they will both slink away....and the older one was not trained using this method! She only witnessed my training the pup, but she knows exactly what this means. She also knows, "WHO dug this hole???" and "UH,OH!!!". They also know, by the infraction, just
who is in trouble. If I ask "who dug this hole?", the older dog submits automatically, while the younger just watches alertly. The younger dog
never digs holes so he doesn't feel a bit ashamed!
Dogs are so much smarter than we give them credit for....it just takes a little one on one, no hitting necessary, good communication.