i am trying to make a 8x4 or whatever is best sized surface that i can shoot off of. i know this has come up many times on here but what material is best for such a thing. and seeing that i live on the beach, my back yard is sand so i need something that is stiff and wont give when i walk on it. i guess i was thinking mounting a plastic like surface onto plywood. i dont know. any help would be appreciated.