I second the black kong. We have one in the kennels for chewy dogs and it has lasted 4 months without a dent so far. Cows hoofs are very good but take them away before they get to small and swallowable.
Cheapest chew toy I use in all my runs is 25mm blue line ( water mains high pressure) poly pipe. Your plumber will sell it. Cut it into 12 in lengths and again remove the small bits.
My daughter mentioned something called a Gorilla. Must be new on the market because I have not seen these yet. Supposedly tested by gorrillas (?) Have to google it.
Border River Pet Resort