its just prey drive, and unless you are there the second they start. you can get rid of the behavior while you are present, but it will never go away when you are gone. They do have rattle snake vaccines, or atleast up here in montana they do. Its not full proof, but it extends the time you have to get to a vet. The snake training they offer out here consists of when the dog gets near the snake they shock with a electronic collar on a very high level shock, so it basically teaches to dog to associate the snake with pain, in return they stay away you hope. I believe the dog knows the difference of when the collar is on their neck and when its off. Good luck and hope that helps a little