stacking live rock

[glarior]

I am going to rearrange my reef aquarium today. However, is there a secret to stacking the rock? I have seen pictures of aquariums having it stacked to the top which looks awesome with all the corals. How do they do that with out it falling over?

I usually stack it on the back glass half way up but thinking of moving it away from the glass so I can clean easier.

Suggestions? Tank has ~23" stackable height and ~16" depth