Forward motion, headfirst & horizontal to gravity!
I bought some protective shorts with padding all around sewn in. I think I wore them under a dry suit; guessing they could go over a suit as well.
Avoiding the rocks is always the best solution ;).
I'm researching everything across the board from mtn biking to motorcross to riot gear. Just bad sh*t luck ... total 4 big hits like this already this season ... same leg same spot, two n the same day.
Problem is the Ocoee is a very shallow and rocky river ... unless you're jacked up on a long board and outta the water its hard to avoid a lot of scrapin and underwater speed bumps. Think I'm cured of RipBoards now for shallow water unless I can find some bomber thigh pro.
Knees and shins are ok w Sis Six One pro ... it's the THIGHS that are gettin hammered.
I've been lucki Guess and have never taken a big hit telegraphing through my Six Six Ones. Thighs ... that's another matter.
This weekend I used Goop to glue Velcro backing inside my wetsuit in the thigh area, and then applied the Velcro stickie to some football pads. Once I slipped the pads down inside and into positiom it worked perfectly ... no pad slippage at all. I didn't think about them again all day long.
I bought a Warrior 'Projekt' Ice-Hockey girdle for rough creek runs. It saved me from a painful injury running the notorious 'Trashcan' rapid in Bailey (IV-V wilderness creek run) last weekend. This can be a rough run, containing sizable drops with a few hidden fins of rock. I hit one hard enough to crack the bottom of a Kern Pro. Overkill for the normal stuff but they can save your butt in the big and manky...
Pads are foam (closed cell) with plastic in some critical areas including thighs, hips, and just above them. They add some warmth and buoyancy, but fit under my suit pretty well. The only problem I've noticed is that the thigh pads tend to ride up. Rob's 'velcro method' would probably help. Sizes run a bit big, if you're on the edge, go smaller (follow the ice warehouse link from above response).