Of the other horses we ride with, he is a perfect horse. Very relaxed and will canter very slowm, totally under control. The minute we drop back behind the lead horse, he is very hard to control. He wants to run right on the front horse's tail and actually slobbers on their tail. I cannot hold him back except to really pull on the reins. In every other way he is the perfect mannered horse. I ride him in a twisted broken wonderbit, which is what he was ridden in when I bought him. I know that he is just young and is probably not used to be ridden on trails and with other horses. I am hoping with more experience he will get better, but I hate to tell other people we have to take the lead every time. Any ideas?