Exercise suggestions?

I am trying to advance my training with my paint horse and unfortunately we bred him as a halter horse originally so his under saddle training is made more difficult...As you can imagine he is very on his forehand especially in the canter/lope (he does western and english so advice from anyone wil be appreciated and most likely tried). I need some excercises that will build his hind end and back muscle as well as keep his head low but keep off his forehand. Any suggestions?

For building muscle, the best thing is to just ride. Not neccesarily fast, just consistently, and enough to break a sweat. Hillwork is good, too. Trail rides build muscle and keep their minds fresh. For his "on the forehand" movement, lots of transitions through all gaits, including backing.

Good luck!

I agree ^^^

I would do lots and lots of circles, start riding in big circles then slowly start making them smaller.

Yep. As everyone above has stated. I have a halter bred QH that is a real bear to get on her hind end. It's a shame too, because WHAT a hind end! LOL.
Trails, hills - making them walk it, rather than trot or canter up, if you have any where that is sandy - that's great, as well as good deep fresh plowed fields, cirlcles, figure 8's, Lots of backing up at stops, groundwork for turning on the haunches, then in the saddle, ground poles, actually, jumping work is good too. Millions and millions of circles. Fun fun fun.