Things I would do differently ...

1. When you measure the foam initially, I suggest cutting it about 1/2 inch smaller all round. This is to give allowance to the cement layering later on. Also, you can easily fill the small gap with more cement later!!!

2. I think 4 inches is a little too thick. The stones seem to "stick out" too much. This is especially the case since I am using a small tank!!!

3. After you seperate into different blocks, don't put cement on the "joints". Otherwise, you will get big gaps when you assemble the parts together!!

4. When carving the rocks, carve larger stones at the bottom. If you are going to put sand at the bottom, you would have already covered about 2 inches of your "stone" wall.

5. The foam is VERY EASY to work with and carve. Might want to consider creating some caves or some way to hide your equiptments.

6. I stuck about 5 layers of thin foam together to get 4 inches of thickness. It was a mistake, as I had to use LOTS of glue. So cost wise, there was no savings. While carving out the shapes, if you did not glue the pieces carefully, the layers will seperate!!. So, start with the THICKEST foam you can find!!!