Strong Horse?

Okay this is going to seem like a stupid post, but im having problems with the horse I loan. He's a 15.2hh exracehorse who I've had pretty much most of the year. When I started riding him, he was really easy to stop, if he went too fast I could just slightly pull my outside rein + he would steady right up.

He's had end of april/whole of may off due to a back injury (so he's been having physio) he's been lunged in walk trot canter + over jumps.
I started riding him again 2 weeks ago.. everything seemed fine; however now when I ask for trot he decides 3 strides is enough, bites the bit + tries to run off!
I've tried the 6 stride thing, + he just clings to the bit + refuses to stop
I've tried differernt bits + nosebands but nothing seems to help
Just wondering if anyone else knows what I can do???

You said back injury... so my first thought is he's still hurting. That's very likely the case. I sprained my ankle five months ago and it still hurts really bad. A friend ripped his ACL in his knee nine months ago and he's still limping. Backs are a sensitive area.... things take a long time to heal.

What bit do you currently ride in? Using an o-ring will prevent him from being able to grab onto the bit, because it slides and doesn't provide something solid.

Also, how are you asking to stop? With OTTB's if you use constant pressure, they will lean into it and go faster--it may feel like he's grabbing onto the bit but he's just being top heavy. If you do a lot of half halts, that should partially relieve the problem. Also remember that OTTBs take a lot of cues from how you sit in your saddle. If you shift your weight back into the cantle of the saddle and sit really deep and low, bringing your heels forward (but keeping them down) they will slow up very nicely.

I also agree that he might not be ready for you to be on his back yet. How long has he been off the track, and what kind of retraining has he had? When I piled on too much too soon onto my guy, he reverted back to what he knew how to do, which was run very fast. You'll need to take more care than usual rehabbing him and bringing him back into work.

I agree with BackInTheSaddleAgain-- his back may still be hurting. One of my horses had a back injury also when he was being trail ridden a lot. He was laid up for 4 months and started back only being ridden for only about half an hour in the arena for a little while then up to an hour trail ride. Now he can do most anything you ask him. If he's not hurting he could just be feeling spunky after having a break.

Definitely another possibility :)

BackInTheSaddleAgain; he's had physio + the vet who have both given him the okay.. when he breaks into canter + starts running he's fine; just very hard to stop
And
justsambam08; he's ridden in a normal eggbut snaffle but will definitely try an O-ring

While the vet may have given him the ok to work, I wouldn't want to canter him for awhile...it takes a lot to balance out at a canter, and horses off the track generally don't do that very well. Stick to walking and trotting, building up his top line and back muscles by working over trot poles, or up hills if you have them. I'd wait at least eight weeks before cantering or taking him over a jump, even a low cross rail.

The canter isnt intentional; that's simply where he's grabbed the bit + ran with the trot he's forced himself into canter.. that's where I have trouble trying to stop him breaking into canter