Under the bit! ARGH

So today I took shad out for a trail ride, walk, trot, a bit of canter and short gallop. Theres a really long road that I ride next to on my way home. We were walking along that and I ask for a trot, and he wants to go running off and I keep asking for trot, so he ends up jogging/skipping/jumping around like an idiot because he wants to run home.
Eventually I get him to trot but he's rushing and bracing against me a bit. So I thought i'd get home and work him a little more, a couple of circles etc to get him listening to me and relaxed. So I take him out back in a paddock, ride him around, he was nice and foward, maybe a little rushed at times but light as a feather. I look down and he's under the bit
He wasnt ducking under the contact, just keeping his head behind the vertical. So I attempt to fix this by pushing him up into the bridle. Nope, didnt work. He'd either bring it up for a second then back down again, or use my leg aids as an excuse to rush off, then when i'd half halt duck under again.
*sigh*
Then I tried doing lots of transitions, that wasnt very successful either. Eventually I got a bit frustrated and decided it was time to get off

See, even though he was rushing, he was tired, but he's the type that will just keep going untill they drop.
So I think the tiredness definitely did contribute to him going under the bit, but I need a solution, especially since at shows he needs a really good work down otherwise we have a nightmare on our hands.

Sorry if that was kinda long, and I hope I explained it well. So, help?

Does he know shoulder in?? I find putting a horse into shoulder in, then turning a 1/2 20m circle, then back to shoulder in for a few repetitions helps to get them coming back up into the bridle as life is much easier when they take a contact!

Try riding him above the vertical. So carry your hands high, push him up but don't allow him to come onto the vertical for a few rides.

Maybe have him long and low for a while. Make sure he continues to use his hind legs and doesn't fall float on his face, but allow him to poke her nose and reach out.

I second shoulder-in. The process of moving the shoulders to the inside really helps fill in the outside rein. Another thing you might try is two tracks on a circle which is very similar to shoulder-in on a circle but with a little more bend at the neck. My 3rd suggestion is spiral in-spiral out. Good luck.

Thanks for the replies! No, he doesnt know shoulder in, ill look into that though, and try the other suggestions :)