Thanks for the comments!! Yea his butt has always been his weakness. I get a lot of people who think he is at least part Warmblood of some sort due to his size and build, they think the Jockey Club made a mistake
He REEEALLY carries himself on the forehand and so he definitley builds those muscles. We are doing lots of transitions and working on building our back and butt up with trot poles and trotting over crossrails. He gets bored so easily though it can only last about 5 minutes before we have to do something else. There aren't any hills around us unfortunatly otherwise we would be doing that a lot. Any other suggestions would be great!