What do you do when your German Shepherd Dog jumps straight up while on a lead? Do you pull down on the lead or do you raise the lead up high? The question is the same for the horse’s head. Do you keep your hands low or do you raise them? The answer for both is to raise the lead and the reins. For the dog, it instantly makes them sit. For the horse it instantly makes them search for contact and this is the clincher… your timing must be spot on… as soon as the horse finds the bit you must ‘give’ with your hands and the horse’s head will lower. It is well known, that a snaffle rein will raise the head and that a double bridle will lower. But do not entertain the double bride until your horse will stay on the bit in self carriage during your entire schooling exercises. You do not want to affect a ‘behind the vertical’ in your search for lowering the head. Look at Charlotte Dujardin, she schools always in a snaffle and mixes it up with BHS and French Classical techniques.
Generally, I’ve found that doing the opposite of the desired behavior is a step in the right direction. So for a horse that brings it’s head up you might bring your hands down a bit to guide them. However, I agree that not letting the horse duck behind the contact is important, but more than moving your hands to maintain the contact, I would think that it is necessary to push the horse forward into that contact with your seat and legs. Sometimes the contact issues really originate from a lack of engagement in the hind end or a stiffness in the back.
Each horse and situation is different though and I think it’s important to keep an open mind when searching for a solution.