Too often, owners, riders and trainers ignore the reason behind a behavior problem and simply slap a "bandaid" on it. Take for example the horse that holds its head high, or tosses it constantly. The common solution? A standing martingale. Hold his head down. The hides the problem, but does not solve it. If anything, it makes the problem worse, and at the very least, causes the horse to depend on the martingale rather than carry himself. Too many trainers never think about the bit, except to try a harsher bit if a horse is too forward, rather than training the horse properly.
Harley was being ridding in a loose ring french link when I bought him, but he seemed unhappy with it. I had been told I could use a Hunter D-ring, but he hated it. Jane looked at his mouth and told me has a low pallet and a fairly thick tongue, and the center joint hit the roof of his mouth. She suggested we try an eggbutt. I found a JP Korsteel oval mouth with a lozenge type center piece, and he loved it. No more tossing his head, rooting, or fighting the bit.
Jane has a great DVD entitled "A Bit of Understanding" that is well worth watching, and could just be the solution to problems you may be having with your horse.