For me it is hard to give any useful suggestions without knowing the situation and the reasons why the horse is bolting. However, in general I guess I focus on prevention more than on trying to stop the bolting response. That is, I try to make sure my horse knows that he does not need to bolt in order to get out of a situation but simply tell me he is uncomfortable and I will do my best to change that.
For example, Summy once did a really cute version of "bucking" in standstill (rhythmically lifting his back for about 5 cm) to show me that he wanted a child on his back to get off. I reacted at once and took the child away, and in the next moment he blasted off in canter. Others here have horses who show them that they want them to get off in other ways, for example by going to a certain place or just turning their head and looking at them. If you encourage your horse to show these signals and then listen to them, I guess most reasons for bolting are eliminated already.
Indeed there have been several discussions about bolting over the last years, but they are hidden in other threads, for example in a discussion about bitless bridles
(you have to scroll down a bit) or in Patrice's diary