@Sniperhank A friend of mine suggested the idea you mentioned about an hour or so before you did. I did that... and well... Lets just say I got about 3 crabs out. I knew from watching the rock carefully that WAY more then three were in, by this point I got tired of it, hooked up a hose and with my thumb, pressurized and BLASTED the rock. More started scattering, I mean to a point I had crabs COVERING my patio. But still the BIG ones I had seen, while rock was in aquarium, had not shaken free.
This rock was a disaster, so I smashed it up. It was then the crabs RAINED out. I lost actual count after 32 crabs. A roommate of mine was excited and all giddy about the crabs and literally ran behind me with a cup collecting some of them, these were some she managed to catch:
One had a very long fu manchu, and was different then all the others:
(The one on the right.) After googling I figured it was a Porcelain crab, and a few minutes after this picture, the big guy next to him ripped off both his claws.
All the other crabs were like the one pictured to the left.
At the end of the day, the rock wasn't worth all the hassle. I tossed it out. I took that one since the guy told me it was his oldest of rocks and biggest. It costed me 5 bucks... (in the snails killed) But other then that, no major harm done.
Thanks for helping me out through my...scare, wish it would have worked out, cause the rock was nice looking.
To bad it was clearly a crab breeding ground!