I mean 1/4 or maybe 1/2 mile and tear up the road that goes to the cave - make it rocky so you can not drag a 2 wheeled dolly with your tanks. I will almost guarantee that will knock most of the "hero's" out of the running. Yes it may be unfair to some cave divers - but you will only being going if and only if you are ready to haul your equipment 1/2 mile to the hole. Aka - you are in shape and you are committed - this is not a half mile walk with full gear on a whim...
Just think about... it is a solution...