Good! Back on topic. I am thrilled that you are, seemingly, at least considering the notion of Catch and Release, norseman. The pit needs to be deep enough so that the Bigfoot can't jump out.
width? the wider the better, within reason, I guess
conceal with material similar to the surrounding area
we could tranquilize appropriately once captured and evaluated, no?
rocks? try a new spot
water? Bigfoot proof bilge pump
humans falling in? private property, no trespassing
night? lights
winter? heat and warm clothing
cave in? doubtful
I don't mean to trivialize those questions, they are good, valid concerns. I just don't see a deal breaker there.