Using your shovel, begin to remove the grass from around the inside perimeter of the marked area. Continue removing the grass from the outside to the inside until the area is bare. Once the grass is removed, start creating the slope from the middle of the trap. Generally speaking, you will want at least a slope of 2 feet. This means the trap will drop 24 inches from the edge of the grass to the middle of the trap. You may decide to add more or less slope, it is up to you.