The pen is constructed of presure treated 4x4's and heavy gage galvanized fencing. Regular chicken wire is not much of a challenge for the local coons, fox and bobcats. The wire is buried at ground level and 4x8x16 concrete blocks line the outside edge to discourage digging. At the doorway thresholds I buried the same blocks to prevent digging there. The pen is topped with the same wire over a 2x4 frame and covered with tarps. I intend to put a permanent roof on over the wire, at a later date. The roof is sloped to the rear to drain off water. So far the pen has proven to be preditor resistant.