I've been riding nearly 50 years (started when I was 4) and I can only think of 2-3 times when a horse deliberately bucked me off. Stopping in front of fences, now, that's a different story - that happens to me ALL the time although less since I switched from hunter-jumper to combined training, since I'm sitting deeper in the saddle and thus less likely to get "launched".
In my case, my dad taught me a 'paratrooper roll' when I was a kid so I roll when I hit. I sent my kids to Aikido training to learn how to fall and went myself for a little refresher . . . they drill it into you until it's automatic. I tripped over my own big feet a few weeks ago and took an ugly fall down a couple of steps. The Aikido kicked in automatically, and I tucked my head and shoulder, landed, rolled, and actually popped back up on my feet. The people around me were startled to say the least. . . . one wise guy applauded . . . so I bowed . . . (did the same thing years ago when a rather tall horse dumped me in front of a fence and I wound up in a full pike layout and landed on my feet) (pure chance but it was funny).
When I first started riding I fell off the mounting block and rolled on my back with my arms out. The trainer stood there with her mouth open. She told me she had never seen anyone fall like that?