i used plastic grids for my base, i also attached 2 and 3 inch pvc
pipes to create caves as well. but then i went to my local landscape center and bought about 200 pounds of sand stone and lime stone mix of sizes. also picked up 6 cans of pond foam. after placing the pipes where i wanted them i attached the rock to the grid useing the pond foam. i painted the pipes using plasticoat paint in flat black. i attached the wall to the tank using GE1 silicon around the top bottom and sides no water gets behind it at all. i also designed the wall to conceal as much "plumping" for the filtration as i could. I love the way it turned out. looking forward to aquascaping the foreground with rock and driftwood. check out my thread "my cichlid tanks" for some pictures of it.
the project was a lot of fun and a lot easier then i thought. for this one being my first i cant wait to do another.
my best advise is to buy a LOT of rock so you have as many choices as you can while placing them into the grid. also my landscaping center charged my .09 a pound for my rock LFS
- $3.99 a pound.... so i also advise you to find a landscaping company that does a high quality pond business as well as they will have everything you need to build this and fish safe as well.
Hope this helps.