I got my 1 yr old Rott/Shepherd two of these balls from doggyloot.com and he has yet to destroy them.
I bought them in April and the one only has a slight crack in it. I shove treats in there and peanut butter and he goes to town on them.
Definitely a must for a power chewer.
Check these out these big super-tough balls here.... Megalast Ball
You can also get JW Pet Company MegaLast Bone Dog Toy
made from the same durable thermo-plastic rubber.