If you check your local sign store (a store that makes signs and posters like what people use to put in your yard when running for a political office) and ask them if they have any left over material. They typicaly make signs out of ribbed plastic. If you put this stuff in front and behind the hay bail then the arrows will stop. It's inexpensive and easy to replace. I've never sent an arrow through a bale with a piece in front and behind. It will probably cost around $15 for a sheet that you can cut to size with a razer.