Step 3 Place the liner in the depression, pushing it to the base of the walls and bringing up the excess material above the height of the walls temporarily. Hold this excess liner in place at grade level with rocks or boards.
With a digging fork or pitchfork, puncture the liner along the floor of the depression at intervals of about 3 to 4 feet. Dont put too many holes into the liner. You want drainage to be very slow. Dont puncture the liner where it covers the walls of the excavation.