Right or left is no importance to a dog. In most basic training, a presented arm is considered the target arm. Most sports and stick work (which is what I assume you are commenting on) are designed to teach a dog to withstand an attack, which is supposed to ensure a dog that is not stick/weapon shy and therefore easily punked out by an aggressive threat with a stick. Some pp trainers are of the school of thought to teach a dog to protect themselves, targeting the weapon arm as well as teaching a dog to transfer its grip to prevent damage. Here are a couple of examples: http://www.youtube.com/watch?v=T2lOrcdndM4 http://www.youtube.com/watch?v=VGuYvC46M68 This is controversial in some groups, and not every trainer likes this method, but frankly, I have seen no problems with any of these methods. Our group trains for contact into an attack on handler. Whichever arm or body mass is present to the dog is getting bit.