The kong type toys are really your only bet if its a strong chewer. They sell a kong that looks like a typical dog bone. It has holes in the ends for putting in treats - our dog has destroyed almost every other toy, except for that one.
Another good option for strong chewers are the nyla bones. They are hard nylon bones. I did not think he would ever chew through it, but he has - they can take weeks of hard chewing before getting too worn down. He really likes it.
Make sure you buy the right size of toy for the dog. Get the biggest size they can actually play with. If they can fully close their jaws on something, they will destroy it. We bought a frog squeak toy that is still alive, because it is too big for him to get a full bite on. He took out all the appendages, but the core of the toy is just too big. He can play with it, but he doesn't destroy it.
If your dog swallows what they chew, do not get tennis balls or rope toys. The rope and tennis stuff can get stuck in their gut.
If it does get string, it may get stuck in its butt on the way out. You are supposed to cut it, not pull it out. I've pulled, but only when it was 'loose'. lol - dogs are great, but you pull a lot of crap out of their butts.
We also have this kong brand food ball. You put dog kibble inside, and the dog has to roll the ball to get the food out. It used to keep him entertained for hours, but he's too smart - he's figured out how to get the food out quickly.
