Only 2.4, shallowest ive had it, but the big rock was above the dog sticking out of the wall of the dig. Looked secure enough, my father got under the rock, up the tube and pull the dog out as she had pushed it a bit further back. Pulled the dog out and the moment he stepped out of the dig, I heard this mighty thud and the rock had rolled into the dig where my father was lying just seconds previous. Very lucky and I've never visited it since.