Nat, it takes LOTS of training and patience for some horses. There is NO short cut to fix that problem. While my qh realized pretty quickly what is asked from her, it took me forever to deal with my paint on similar problem (and we still are working on it, after 4(!) months of lessons with dressage instructor).
Don't use any gimmicks (especially if you don't know how to use them in 1st place), only correct riding will help with the problem (having a good trainer is very handy too
). When your horse drops the head and comes on bit don't let go the rein, keep your leg on and drive him into the contact. You can also check similar threads in "English Riding" and "Dressage" sections of the forum - you'll find lots of good advices by very experienced riders/trainers.