I really think you should get some plastic crates. Seriously haha. I know ive mentioned this before but with more rocks comes more concern.
It wouldnt be too difficult to remove all your rock, slide as much sand to one side, and wedge the crates down into the rest of the sand as far as you can, preferebly to the glass. Then do the same on the other side.
You'll be a lot safer and sleep better if you do, i promise!