I was asked by a new customer to submit a proposal from a design idea I had for her front hill. The hill is very steep, rises 12' over 30' in one spot then softens from about 18' over 70' in another place. You may be able to tell from the pictures what I am talking about. She would like a large boulder (2'-3') wall like my plan below, I have never heard of an engineered dry laid boulder wall, but I am thinking I should contact an engineer prior to estimating. I am not sure if I am being too cautious or not. Have any of you ever laid a 2 tier boulder wall? I am just looking for some input. The bottom wall (neither wall is shown to scale) will be 90' long by 4' high, and the second which will be about 8 ' away from the first if 70' long by 4' high.