I've seen other guys around here do this and I am thinking of doing it myself. If you have a home and farm store like Tractor Supply Company, Orschelns, etc. they have very LARGE pieces of styrofoam that small trailers, Bush Hogs, etc. come packed in. They'll usually give it to you for free from what I understand since it is just trash to them. One section of my old archery club actually used this and glued the blocks together with liquid nails and staked it to the gound. It was real sturdy and stopped everything you could shoot at it. They used it as a backstop for a smaller 3-D area for those that didn't want to walk on the trails and to shoot at moving/swinging targets.