We have a Pyrennes/shepherd mix that chases any raptors or other large birds that fly over our 5 acre property. I don't have my chickens yet, but I'm thinking he will be good with them, if we let him know that they are his herd to protect. Maybe you could teach your dog, also (if you have one) - I started just by encouraging him to chase the pigeons out of the barn, and he eagerly took it from there. I used to have a German shepherd in Indiana (lots of redtail hawks) who was out with the free range chickens, and I never lost one to a hawk. (Nor to the dog)