Maybe I am being naive (not ever having been at the bottom of a 12' hole), but couldn't you just climb out of one?
I have done a reasonable amount of rock climbing in my time and know that you can hold and balance on some pretty tiny protrusions.
I mean, couldn't you kick little divots into the wall and use them to climb up?
Ok, this has me thinking. I think I gotta go find a 12' hole somewhere and try to climb out of it. Curiosity and the cat, you know.
I suppose you could try to climb out.
I am not so sure I would want to try fearing a cave in. The divots would work for your feet, what would you be holding on to, to kick the next set of divots? I have never seen anyone climb out of the ones we dug in the jungle, they were made for killing. This is the first one that I have made for catching and he didn't climb out. I don't know how long he was in the hole, it was checked three times a day.