Just a little advise I received from a friend that owned a bow shop. When the Block 4x4 target starts to wear, fill the inside with the expanding foam, take a a drywall knife and scrape the excess off to get a smooth surfuace, take a trashbag and put it over the target and lay a piece of plywood on top with some weight added to the top of it. When the foam tries to expand it will be compacted inside giving you further use out of the 4x4.

He used to use this technique on his block targets he used for the shop.

Hope this helps for the worn out 4x4's. Happy shooting!