Your horse needs more basic training. You shouldn't have to ride out your horse's bucks. It's up to you to do more training. Your horse is telling you if he is nervous about being ridden. NO horse will just throw you "out of the blue" without signaling first. Think about what sets him off. I would take him back several steps in his training and solidify his ground behavior and his behavior under saddle before you mount. It makes you smarter to look back at your friend's injuries and realize that you don't have to end up hurt by your own horse.
Look into ground training. It's always better for a fresh horse to buck on the lunge and get under your control that way, than to wonder when he's going to act up.
Oh, I thought I stated that when he's being lunged he bucks cause he's fresh? He hasn't bucked under saddle in well over 8 months, and that was my error.
This is just a thread of me being paranoid that something will happen because "bad things come in threes" and horses are unpredictable. I haven't really had any problems with this horse under saddle that wasn't corrected with some leg.
Other horses however...