When we bought our house it came with a very nice play area which also included a sandbox. The sandbox was not in a good location and the only thing it was good at was growing mold. Megan came up with the great idea of moving the sandbox and changing it to a rock box.
My Dad was able to help me with this project which was a HUGE help. I had to modify the original design to make it more functional for its new location. This included a few pressure treated 2x8s and a pressure treated 4x4 post.
Once we had redesigned the box, we were able to move it to its new location. We placed some landscape fabric and then 25 bags of pea gravel to give us our rock box.