That is exactly what I'm dealing with , the speed at which it happens sometimes all you have time to do is to try to stay on.  If any one gives you any good ideas let me know. Sounds like my guy and your guy both react the same way.  Now if I could just convince him to trust me like my mare. She'd stop, look , then look back at me to see what I wanted to do. I wish I still had her.  Both were resessive types in the herd to.

 Yesterday I rode my horse at an arena and then drove him.  The arena was next to a very large grandstand with metal bleachers.  When we arrived no one was there except us and I handwalked my horse around the arena several times picking up odds and ends of wire and rock to make it safer.  Then saddled and after a light longe mounted to ride.  i was working on relaxation to prepare him for his first drive away from home.  Our ride went well until some workers arrvied and begain making noise and then some children wh began running in the bleachers.  My horse would react to these noises and was very unwilling to be on the side of the arena where they were comming from.  When I got him busy on the bit doing shoulder ins leg yeilds and turns on the forehand in motion he seemed to not even notice the noises or people.  Wehn we bagan to harness he stood quietly but did flinch occasonally as the children ran and screamed on the bleachers.  Of course I asked them nicely to stop and they did for a short period of time.  Through out his harness session they would begin to run and then as we asked them to stop they would settle down.  My horse was so focused on his harness work and listening to my voice he did not one time spook of even appear to hear the kids. ..From this I again learn that when my horse is fully engaged with me the outside world does not interfere with his work or scare him in the least.  When I let his attention wonder even the slightest he looses that focus on can get spooked by his surroundings.  The difficult part is to do the free walk with him still focused.  In all othe gaits he is usually totally with me.  I also must be totally with him and not get distracted by the environment.

I was just talking to Jane Savoie the other day, and she told me she has a new book coming out on 101 Ways to Get Your Horse On the Bit ... And Keep Him There. You might want to keep an eye on her Web site at www.janesavoie.com or follow her on Facebook for more info. Can't remember if she said it was going to be an eBook or an actual book.