But his trot/jog is way too fast. It's to the point it becomes jarring and quite uncomfortable, if not nearly impossible, for me to sit without bouncing all over the place like a maniac.
I find myself pulling on his mouth to slow him down and I hate doing that, especially with the tom-thumb bit the barn owner uses for him (I don't know if it's my place to ask to use a different bit; I don't want to seem like I'm intruding on how they care for their horses). In lessons I ask if I'm being too rough on his mouth. They say no, however I still feel like I am when the reins are tight and the horse is pulling away. I ride Western; I shouldn't have to use that much contact with a Western horse. It's not his fault of course, and newbie me is trying to figure out how to solve this issue. The BOs say he was probably used as a Barrel or Roping horse in his last home and only trained to speed.
When I'm riding him outside of lessons, I've tried a couple of things to slow his trot down. One was to completely stop him everytime he went too fast. This is what I'm also told to do in my lessons. This seems to frustrate him even more, causing him to go faster and step heavier at the trot. I tried trotting for very short distances. Also seemed to frustrate him quite a bit.
So today I tried something different. Circling like there's no tomorrow. As soon as he speeds up we do a few small circles. This sends him into a lovely, comfortable trot. As soon as he does it I let off the reins completely and say, "easy" in the hopes he will make the association that "easy" means "I want you to slow down and go this speed when you're going to fast". After one or two circles we go ahead again until he speeds. Then the process repeats.
This seems to be getting some results! But (after my long post...sorry about that) does anyone have any other advice or tips on what to do with a speeding horse?
Okay, jarring and uncomfortable sounds like it's an unbalanced trot which coincides with what you are describing as "fast." When you begun the lease, what did the OWNER tell you was the training level of this horse?
Stopping him when he goes too fast is just putting a LOT of pain on his mouth, therefore when you go to move again, he's already bracing and anticipating that you're going to pull him back into a halt again. If you are going to stop him, spiral him with your body and an open rein so he goes from a large circle to a tiny circle and eventually a stop.
If you circle, circle with purpose! I like your idea but he's probably blowing you off. You need to be consistent but not monotone. Horses get BORED of monotone
Do some circles, but maybe work some figure eights in there too, or a half circle to reverse, or get him back down to walk, or weave, or do any lateral work that you know.
Your goal is ANYTIME he isn't paying mind to his speed and feet, re-focus him. Give him something to do besides going straight. You know when you drive and it's a straight rode; no curves, no tunnels, no beautiful scenary? And you get really really bored and try to turn on the radio to keep your focus on what you're doing aka. Driving?
That's what you are doing to your horse atm. He is trying to go faster because he's hoping he can canter because it's different than trotting, or that he can be the boss and make decisions. So mix it up. Put in some circles, weaving, leg yields, poles to trot over, etc.
When my horse was VERY discombobulated trot (and he's green so this is different than a trained horse) I kept up with him at first and slowly asked him to do things to slow him down. When he got there, he got a release of a short rein. Do you do anything to reward this horse once he gets down to the speed that you like, OP?