ALL above is useful advice. I would add that we push hard to get our horses to want to charge to the fence and over that they forget about listening to your halt aids. THIS is why 3 day eventing includes Dressage. It shows obedience to aids.
I would suggest that you go back to schooling on the flat. Teach your horse to listen to your WEIGHT aids, by practicing them. Also, Start with half-halting and transitioning down, canter to collected canter to posting trot to collected, sitting trot, free walk to collected walk, to full HALT for at LEAST 15 seconds, then back 4 steps, halt on loose rein. You need to give your horse a chance to realize that this is also part of what is expected. After jumping courses awhile horses get really heady and they pride themselves on doing the jumping job right. You want to keep that and train for the other.
Additionally, break up the retraining by asking in different places in the arena. Add side passing. Halt with the nose in the corner, and turn on the haunches to change reins. Halt after a corner, back to the corner and turn on the forehand to change reins. Serpentines between and around the poles on the ground. If you horse gets REALLY confused by any of this, dismount and cue and lead slowly to teach an exercise, then re mount and try again. =D
If you don't understand how to correctly half-halt, please post and somebody here will explain. (I'm busy with business so I may be offline.)