We have an 8 month Golden that when walking can be fine one minute and then start to jump and bite (not playfully) for no apparent reason. This has been known to carry on for up to 10 minutes before order is restored. We have used a muzzle and he seems fine after wearing this for a while. He also has done this at training classes when on his lead also for no apparent reason. At home he is better but has his moments. Basic training is OK, sits,stays,fetches etc just seems to be when he is on a lead. Can anyone think of ways for us to stop this behaviour when out