To correct a horse that pulls after jumping a fence, you need to practice downward transitions to the halt after jumping each fence, until the horse learns to anticipate collection after the jump. This type of work–pulling the horse up after every fence in schooling–may seem tedious, but is very beneficial in training your horse to have an automatic response of collecting after the fence.
You may need to apply a pulley rein at first, if the horse is very strong. Make sure that your reins are quite short before you try this. Then place one hand in the dip in front of the horse’s withers, while slowly and steadily pulling back with the other hand. The fixed rein position of the hand placed in the dip gives your other hand added force when you pull back. You should be sitting during the application of the pulley rein, so that your back reinforces your hands, if need be. Also, the hand in the dip MUST REMAIN FIXED. If this hand slips and you’re only pulling back with the other hand, you could cause the horse to fall to the ground. (Look at some old cowboy movies and watch how the stuntmen cause their horses to fall by pulling hard on a single rein.)
You may need the pulley rein the first time or two in order to pull up within four or five strides of the fence. The horse should catch on to your routine and begin to anticipate the command to halt. Any slowing of pace or softening of the horse’s mouth should be rewarded with a lighter feel of the reins. Remember, horses only know they’ve performed correctly if the rider shows a clear differentiation between right and wrong by a softening of the aids when the horse gives the proper response.