I have a customer who is asking me for some advice. He has a mound of dirt in his back yard about 15x15 by 4 feet high. There are trees surrounding all edges. He wants to put a brick patio on the top of it. But first he will have to square it off a bit. Can he bring in sand, and build up the sides? or will he have to put in a retaining wall around all 4 edges? If he has to put a wall in, what are his cheaper options besides the brick wall?