Nothing wrong with protecting your valued birds. They certainly can't defend themselves.Get a pellet rifle and shoot the dog so it learns to stay away. No harm to the dog.. just gets the point across.
There was a dog from down the road that killed many many chickens this year before we got the culprit on camera. We warned the neighbor that if the dog came back we would shoot to kill. She hasn't been back since. The guy got rid of her. Poor dog but it is what it is.