I agree with EagleViewArabians (sorry, can't call you EVA-makes you sound like a disease)
I know how much everybody hates this, but I HAVE been riding and training for over 40 years, starting on OTTBs and OTSBs, the only ones that ever really gave me trouble bolting. A horse that is truly out-of-control bolting is not going to respond to a squeeze and a pull. Squeeze a OTTB, you're going to go a whole lot faster, and they pull like freight trains. OTSBs, they just don't much care what you do up there. The only way to stop them was with one rein, or a pulley rein on the less determined ones. I was riding a SB once on a back road, and the moment I turned for home he was off. To get to his barn, he would have had to make a 90 degree turn, with barbed wire on each side. I had to take one rein in two hands and use my full weight just to keep him straight- his head and neck didn't come around at all. Of course he stopped as soon as we passed his road. Guess he had a history of doing that- so they told me when we got back.