Whichever is cheaper and/or aesethically better for you, ideally sheet metal or acrylic/perspex/plexiglass for durability and long term, but can use sheets of wood as well, placed at least 2-3 inches into the ground and a foot and half up is what the agricultural dept recommended here at one point when I had a problem with snakes going after the coup and pen. It took care of the problem. To also make sure any holes and crevices are sealed off for the coup in floor boards and by posts, if the coup is not surrounded by fence. My neighbor had a problem with this, as it was a raised coup and they would climb the posts to get in.