My 8 year old australian shepard has a very strong herding instinct and has nipped quite a few people on bikes and joggers. Animal care and control has ordererd me to keep him muzzled but he really shuts down when he wears it. How can I break him of this habit? Its very discouraging [img size=227]http://www.trainpetdog.com/elitedogclub/images/fbfiles/images/running2_edited.jpg[/img]