I anticipate that my horse is going to buck which makes him do it. What can I do to stop this?

Also think about why he bucked. When my horse bucked me off there was many questions I asked myself: "Does his back hurt?" "Was I pulling on the bit?" Etc.. And his back was the problem. We had a chiropractor come up and they fixed him right up. He hasn't bucked me off or even bucked really since then and that was like the first 11 months I had him. I've had him for 3 and a half years now.
I've been bucked off before. Its not fun, so when he bucks now and he puts his head down, I sit back and pull the reins up. Horses can't buck if their head is up.
If you can ride the buck out than do that. Tell him to keep on going forward. If he has enough energy to buck, he obviously can canter for a long period of time. After he is exhausted and stops throwing his tantrum. Let him know that each time he bucks or when you anticipate it the consequence is only more work.
Literally try and picture him being calm and relaxed in your head while riding him when you get anxious about the buck.
Relax and be calm around your horse. If he does buck, then do a one-rein stop to get him back under control.
Relax your body, and when you feel like he's gonna buck kick him forward