What's interesting is that I can stop him as fast in the French snaffle as the kids can in the gag. It's just when he gets rolling after jumping 3-4 fences he gets kind of excited and above himself and it takes me 5-10 strides to get him stopped. But he used to grab the bit and bolt after every fence, he's not doing that any more. When he finally just cantered sedately away from a single rail, I patted him and praised him, jumped off, loosened his girth and put him up. I'm going to go out Friday and work him back and forth over a grid at a slow trot, and just halt him as soon as he clears the last cavaletti. Sooner or later, he's BOUND to get the message!
I think a gag is sort of overkill, but it's adjusted down to the first ring and the kids aren't allowed to hang on it. (And when I say kids I mean the teenagers, not the little ones, everybody's looking young to me these days.)
Well he sounds like a super boy who WANTS to be a good horse. :-) I hope that you have fun with him.