I have a 6 year old ottb(off-the-track-thoroughbred). When we rescued him, he hadn’t been ridden in a year. He had only been raced 6 times. I love this horse! He is the most loyal fun loving horse I have ever had! He loves to be ridden and loves people. He just lights up when he sees me coming with my helmet and bridle (yes, he actually likes the bit!) I ride him in a plain sweet iron snaffle with copper inlays. He loves to be ridden. He is so sweet under saddle and tries so hard to please. He is calm and eager in his work. Nothing like the stereotypes I’ve heard of ottbs.
My problem however is that he was trained just like a race horse. 2 speeds walk and run. Absolutely no heed of leg or seat (he has come along great with that though), and a hard heavy, unresponsive mouth. I try to ride natural. Doing plenty of flexing at a stop and working on one rein stops at a walk but for the life of me I cannot get him to drop his head and give in to the bit. He likes the bit and I refuse to use anything harsher than a snaffle. He flexes fine but I don’t know how to ask him to give to the bit instead of matching me pound-for-pound when I ask him to give. This is not about head set for show. Just so I can make him safe when I ask him to stop and so he will drop his head a little so he can see where he is going on the trails. I would like to show him but that is not and never will be a priority. I’m just trying to further his education and make him safer. But I don’t know how to ask him to drop to the bit. He just seems to take it and run."
Unfortunately, if you plan to show your horse you will have to use a bit. However, in the interim, I would suggest that you try a Dr. Cook Bitless Bridle to accustom your horse to weight and leg aids and you will not be forced to pull on him with a bit in his mouth. This would only make matters worse.
He may well have mouth ulcers and other damage to his mouth. At the very least, he will have to heal. None of this, of course, is his fault, but the fault of people who put money and ego first before the feelings of an animal.
I would get him lunging quietly first. Correct lunging is VERY positive for a horse, usually much better than round penning. Also be careful of the one-rein stop business. This method for some reason has really caught on, mostly in natural horsemanship, but it is really overused. It should only be used in an emergency situation.
You need to start from the beginning with this horse. He is indeed fortunate to have you as his new owner.