I have an estimate to put together for a guy who lives down the street from me who wants to do three seperate retaining walls in his backyard that is heavily filled with trees and has heavy clay. The longest wall will be about 70' long and will only be about 1' in height winding in and out of various trees. The reason for the walls is 1. Erosion control and 2. Looks. Directly infront of the wall he wants to do a 'dry creek' I say dry since the walls will collect all the water and direct all water to a seperate area. The dry creek is to go along the 70' long wall and be approx4' wide with a swell built in and it is to be filled with #2 limestone approx 3-6" in size. My only question is should I lay mat down first to keep the limestone from sinking in the heavy clay and to prevent it from getting dirty, prevent weeds, etc. or is it unnecessary and insufficient to hold up to the size and weight of the large lime.