Our heeler is now almost 1 year old and does well with most all other people and animals until people start to "fight", act excitedly, and use aggressive voices, or until someone moves close to me to give me a hug, especially larger males. When this happens he tends to nip or lightly bite the other person involved. It is difficult to stop him because he rarely gives any warning signs. Does anyone have any advice on how to control the biting and/or teach him that it is ok for other people to be around me??