Advice on training equipment?

Last year, I rescued an amazing saddlebred paint in his early 20s. While I've ridden for most of my life, I've never owned or trained a horse before. He was a barrel racer in his younger days, and has some bad habits. I'm hoping you all can help me figure out the best tack adjustments to help me retrain this fella so that he learns to relax and smells the roses a little more.

Being a barrel racer, this guy's favorite speed is GO! I can get him into a walk or trot, but he's constantly trying to move into a canter. I've done lots and lots of slow work with him, but as soon as we try to speed things up a little bit, he forgets everything we've worked on, grabs the bit, raises his head and runs! Even when we're just walking-walking-walking, every few steps he's trying to break into a jog or lope. I use the see-saw technique to get him to lower his head in a walk and trot, but when he's cantering, nothing phases him.

I've also tried to keep him engaged by cantering serpentines, circles, direction changes, etc but as soon as my guy gets a chance, we're off to the races again.

I prefer riding english, but I do have a western saddle. I have a snaffle bit on him right now.

Various people have suggested: Using a training fork, getting a martingale, using a tom thumb bit, using a hackamore... I've done my research, but for every person that's said, "This is a great training aide", there's another one saying "Noooo! Don't do it!" I also don't know if I need additional tack for these things (do I need a breast collar to attach a training fork or martingale to?)

So! I'd love to hear what you'd recommend so that I can finally make some progress with this guy.

Do you have a wood fence, panels or barn wall you can work along? Start walking along the rail about 6-7' off on a loose rein (use a snaffle). The moment he tries to pick up speed, turn him toward the rail to reverse direction. He'll likely stop and that's ok just ask him to complete the turn and walk on. Move away from the rail again. Just keep repeating the turn-backs until he will walk as you ask. Give him a break for a few minutes. While this is fresh in his mind do this at the trot. This is also getting him to collect. Once he will hold the trot for half a minute. Put him away. He'll need the rest as his hind end has worked hard and as you say he's in his 20's. For your next few rides, don't canter but be prepared to do these exercises again altho it may take only a few turns to remind him. You want this exercise to override what he's always been told to do.

Thank you for the tip! I'll give that a try. I've started volunteering at a big, busy barn today, and ran into an old friend that's going to give me a hand with training as well. She's going to bring a few pieces of equipment to try and see if it helps *fingers crossed*