These marks indicate where the top of the fence will be.
Baby wipes are great for removing pencil, chalk or crayon from walls.
Place a strip of tape horizontally across the marked area. These strips indicate the outline of the pickets. In each of the areas between the guide line and the picket-top line, place two small pieces of tape diagonally to form a point like the top of a triangle. These are the outlines of the tops of the pickets. Remove the horizontal guide tape and replace it further down the wall.