A Bucking Horse

Question
A couple summers ago I adopted a rescued horse who as far as the rescue center and I know was just neglected but not abused physically. He's a 7-8 year old paint quarter horse and we have him under saddle and trail ride him a lot. Just recently though he's started a very bad habit. If he gets into any speed above a trot he starts a bucking fit. I've been able to pull him out of it all times but yesterday he finally threw me.
This is what we were doing prior: My dad and I figured we'd ride him up and down a fence line just to gain some sort of control. I'd stop him, back him up, and turn him on his hind quarters. That was all fine. I had him trot and I stopped him halfway down the fence line. I walked him a bit further and asked for a trot again. That's when he bulled up and away we went on another rodeo expedition.
We ride with a snaffle bit and he's had his teeth floated. I hardly think it's a medical issue why he's bucking. I say this again, this just recently started up maybe late winter, early spring. I've ridden him in a canter and gallop before so I don't know what's wrong now. Do I need to lunge him in a canter? Or do I ride his bucking out (if I can stay in the saddle).
Please give me your opinion
-Sarah

Answer
Hi Sarah,
If you have ruled out saddle fit or medical issues, then this leads me to believe the horse is just saying, "Nope. I ain't loping!!!"
I suggest you find an arena. You need to be in a controlled environment to work with your horse on this issue. Cue your horse into a lope. Lope for about five or six strides and then one-rein him to a stop. Keep doing this until he lopes off without bucking lengthening his distance in a lope. Make sure you have your one-rein stop in order and be prepared to do it if his head should drop between his legs. If he is just cow-kicking out at a lope, give him a little spank of the withers each time he does this and ride him through it. He should learn that kicking up or out will not get him out of his duty. Don't worry about steering your horse while doing this. Let him lope off anywhere he wants to go. Just cruise around the arena without steering. You can add the steering later once he gets out of this habit. If you feel you can't stay on during this exercise, find a friend who has a good seat or hire a trainer who can come out and ride him through this. No need in you getting hurt. You can't ride your horse if your laid up in a hospital.
I hope this has helped you. Good luck and please stay safe.