I have a thought to simplify/complicate things. I have toyed with the idea of using a petzl mini traxion pulley/ascender and attaching foot loops to it for glacier travel. If someone goes in, you arrest and place an anchor, then clip the leg loops (attached to traxion) into the anchor. At this point, you already have the ratchet component of the pulley system, and just need to finish off the rest of it. It works as an ascender as well, so if you fall in, you can get out. Seems to work much smoother than the autoblock system, and I find that if you need to work a tension release mechanism, it simplifies things a bunch. Problem is that it's a pretty heavy peice of metal to be bouncing around your crotch when your just walking. Anybody have any thoughts on this?