I would put ground poles before and after the jump. It really helps with my horse.
Ground poles :)
We set one ground pole a stride or a bounce before a 70/80 cm and we make them trot into the pole to then take the step to jump over the jump- engaged the hindquarters and works on the horses basquel- you can then come in at a canter and put the jump up if they do attempt to rush- or add more poles to get them thinking :)
An excercise that you could do is set up a jump on the diagonal. Then start making trotting circles, when you get in line with the jump go to it but continue your circle before you get to the jump. Then work your way to doing this at the canter. You can definitely mix this up and jump it once in a while and have mixed patterns so your horse doesn't catch on with the pattern. We had to use this with a horse I have ridden and it has helped. Another thing that helps is just sitting back and waiting for the jump to come to you. Hope this helps!
Grids! Lots of grids. They'll make him think about where he's putting his legs and if he goes too fast, he won't be able to do it, so he has to slow down a little
A pole 4 strides before and after your fence
Have you tried ground poles? If you space them together right, your horse can't rush them without hitting the poles. My moms gelding did the same thing, we tried this. It worked well for him.
I have a horse that did this, try after a jump getting him to trot, walk and halt so he doesn't take off after a jump and listens to your leg and hand aids. Also then try a combination with about 4/5 strides between each jump. If he rushes at the second jump then pop him over the first and ask him to trot, walk and halt in the middle of the combination. Do this several times until he is listening to you rather than focusing on the jump, then try both jumps together and he shouldn't rush at the second
Similar to the other answer, I would set up take off and landing poles to force them to think about where they are going. Also grids are great
Hi! You could try putting canter poles in front of the jump so the horse has to pay attention and watch where they're putting their feet, or create a "bounce"/combination jump so the horse has to focus on what they're doing rather than going fast. There are lots of exercises on YouTube that you can easily find. Good luck :)