Bad Brig

I have figured out how to make Brig buck! He has bucked two more times since I mentioned it before. Each time basically the same thing occurred. I was trying to turn a circle at the canter and he was trying not to. I asked him to canter a circle to the left and he would turn his head left but his shoulders and then body would continue mostly straight despite the fact that I was using my right leg and rein to prevent this from happening. He basically ignores my outside aids (and others) whenever he feels like it. So twice now I've tapped him on the shoulder (the right one in this case) to make him listen to my aids and to help him understand that his shoulder shouldn't be going straight or to the right. Well, apparently he really doesn't like being tapped on the shoulder with a whip. Both times he bucked. His bucks are actually kind of fun though. Not scary at all. I think that maybe he might be able to teach me not to be scared of horses that buck. His are sooo easy to stay on. I don't know how big they are as I never have any witnesses but I suspect that they were decent even though I didn't lose my seat at all. Anyway, although his bucks are not scary his bolting kind of is. I don't mind at all it if I'm in the arena by myself but yesterday one of the girls was in there with one of the ponies. Almost as soon as they came in Brig tried to take off while we were cantering. He never goes far and I always try to steer him into something or circle him but he's really quite strong and he doesn't give to the bit as he should so I really don't have a lot of control. I was concerned yesterday that he was going to go after the pony. He is so aggressive with other horses that I don't trust him at all around them. If he actually tried to attack one while I was on his back I'm not sure that I could stop him. Yesterday was the third time in the past few weeks that I've been concerned that he was going to go after another horse. I really need to find some way to get him socialized so that I don't end up with some crazy horse that can't be turned out or ridden with others. After the one bolt he was fine and didn't try anything else but one is too many. At the end of July I need to find somewhere to keep him for a couple of weeks because the people that take care of him will be on holidays with their horses. I am considering asking the people across the road if he can go in with their horses. They have a few large fields with lots and lots of horses. I figure if he's in a big space with so many horses that he can't possibly control and chase them all it might teach him how to be a horse. But I don't think that he will hold his weight if I put him out in a field like that. I'm having trouble keeping/getting him fat as it is. He gets lots to eat but I think with him being a young growing gelding he is just using it all up. It seems to me that it is often difficult to keep weight on young geldings. He's not skinny right now but he's not as fat as I'd like to see him either. Maybe if I really pour the food into him for all of June and July he will get fat enough to last a few weeks across the road.
The other horse that I've been working with has been doing great. She is doing walk and trot with no problems. I was trotting on her on only my third time working with her. Tomorrow I'm going to get her owner to get on her and then on Saturday we are going to take her on the trail. I will ride her and he will ride one of his other horses. Then if he thinks she is good enough I will be done. I don't mind doing more with her but I think that he should be able to do the rest on his own.