The 2 on the very top rest on the glass, the 2 small ones in the right corner rest on the glass, and the one on the far left on top rests against the glass.
All the rest are stacked. I have a good 3-4 inch passage way behind all the rocks. The starfish and shrimp love to hang out back there !!!
A guy at my office offered $200 for the 1 big one on the bottom right. You can't really see it in the picture, but the 2 real dark spots in the middle are actually 2 holes that pass through the rock. 1 is about 3" and the other is like 1.5". Then, the 2 dark spots to the right of those is 1 big hole that goes down through the bottom and out the back. My largest peppermint will attack anyone that goes near !!! Guess he has little "pimp pad" down there. I have a powerhead pumping through the smaller hole in the middle and the clowns abosolutely love it !!!