Uh...sometimes I rap down stuff that I cannot climb back up...stuff like .12 or .14 or even overhangs.  So, my original question, how often does a fifi hook or skyhook get dislodged in a rock crevasse requiring you to climb up to dislodge it?  
  
Well, I use this technique at least 5 times a week, maybe 6, and it has only happened to me once and that was when my stupid partner pulled the rope the wrong way. So I just said "Ok fool leave it fixed and buy me a new one."  Light and fast!  
  
It's not the only technique one can use involving a hook and a line