I had an awesome Cattle Dog that could care less about the chickens. Chicks on the other hand she was ready to snack on. I have a new CattleDog girl who is showing a bit too much interest in the chickens.
As you have seen in these posts, training, TRAINING and MORE TRAINING is what is needed. Personally I believe larger dogs, Pyrs, Mir's are great flock dogs. Borders are wonderful animals who if trained to work stock will not let you down. Honestly, other than Borders, dogs with high prey drive are going to be very iffy around any stock unless trained extensively. My first CattleDog girl was my trained Service Dog, would do anything I asked on the first command. Would stop on a dime. Parents wanted me to train their kids after seeing her work!! But I would never have left her alone with chicks or young ones.
The thing to remember is a dog is a dog. No matter how well trained, it's still an animal with basic instincts. If something happens to your chickens because of your dog, it's not their fault. Not really. They are dogs and nothing more.