When you get back to your fence work, use your new flat work to collect him before and after the fence. When he rushes at a fence, collect him more, transition down, or (if you have enough room) turn and circle.
Using gymnastics also helps with a horse that rushes. Set up a long line of small obstacles, like a canter pole to a cross-rail, bounce to a small 1' or 1'6" vertical, one stride to a cross-rail, bounce to another cross-rail, with a canter pole at the end. These kinds of gymnastics will force your horse to slow down and think about the obstacles. BUT, it is very important NOT to put a horse that is a bad rusher through a gymnastic right off. If you do, you risk a bad wreck in the middle... You need to go back a few steps and get your flat work down, so you can control him within the gymnastic.
A new bit can help, but training is really what your horse needs. I personally would use a kimberwick with a roller in the middle. That would give him a mouth piece like what he's used to for flat work, but a bit more brakes. Like this one: