dog toys for german shepards that only chew??

As I put into the cruncher the mangled by dog Ultimate Boomerang, I wondered if there is a toy that our 8 month old male German Shepard cannot destroy? Until told otherwise by our vet, we had given him pieces of hard wood with iron on one side. Our dog is dedicated to chewing! Our Shepard at 8 months is 92 pounds of muscle with large jaws that love to chew constantly. Any suggestions?