Here's a way to build a quick rock ledge using some crushed gravel and aquarium silicon.



Take some crushed gravel and outline the form you want the wall to take. Using aquarium silicon, attach the first row of gravel together to form the base of your wall.

Then start siliconing subsequent layers of gravel on top of the base wall, minimizinng spaces in the wall.





Continue to build up the wall until you reach your desired height. You may want to thicken you wall to reinforce it if you want a really high wall.

When you are finished, allow the silicon to cure according to the directions.