One of my go-to exercises is a one stride set with large crossrails (quite large - like top of the standards large) with a placement rail before, in between and after. Depending on the horse’s stride length and how much you want it to compress I would set it at either 18 or 20 feet, with placement rails at 9 or 10 feet.
So it would go placement rail, 9 feet to the crossrail, 9 feet to a placement rail, 9 feet to a crossrail, 9 feet to a placement pole.
This keeps them super straight and really makes them rock back on the hind end. I personally think it produces a better effect through the hind end and haunch than straight bounces because it’s a little more practical - while I like bounces for certain things I think they can back off or get a bit stabby up front with them. I like the above exercise because you’re really riding a one-stride, so it’s more fluid, but the high crossrails and placement rails gets them to really rock back and use their bodies.
You’ll need to place with the distances a bit depending on the horse’s stride and whether you want to trot or canter in, but don’t make it too long - I’d say no longer than 22 ft cantering in, otherwise you’ll lose the benefit. You want it to feel short enough they really have to use themselves well - but not so short that it’s impossible or that they lose the fluidness.
One more - set a single jump in the middle of the long side, with a placement rail 4 or 5 strides before (depending on space) and another placement pole 4 or 5 strides after. The goal is to be able to ride in and ride out with the same amount of strides before and after. This really gets the shape of the jump and the balance before and after the jump correct.
If your jumper loves his forehand, he’ll probably land and want to drag you or land and be unbalanced and rangey. If you’ve set them as 4 strides, the 4 riding up to the jump may be easy, but getting an equally even 4 on the back side probably won’t be as easy. It’s deceptively simple unless your horse is well schooled in consistency, balance, and straightness. Play with the single jump to accentuate the problem. If he’s having trouble containing himself initially, set a single tall vertical. If he finds the vertical easy, set an oxer to challenge him on the backside. Once he does that well, widen the oxer or set a triple bar. Or get 4 strides on the way in and add a stride for 5 on the way out. Or ride in leaving out in 3 and get four on the backside. This one came from Greg Best and I love it!