Old sails
I have two big Labrador retreivers who tore up every bed we bought or made for them. They are past the chewing age and never put a tooth to anything else, but after happily snuggling down at night, the next morning the new beds would be trashed. After last year's hurricane Ivan, my old genny was pretty tore up. I salvaged enough to make two 3 ft. sqare envelopes, stuffed them w/ old blankets, and Rambo and Barkley have not put a mark on them.