From your dog’s perspective, if it’s on the floor, it’s his. It’s so obvious to us that some things aren’t meant to be chewed that we sometimes fail to see that it’s not so obvious to a dog.
How is he supposed to know the difference between that old slipper you gave him and your $100 running shoes? The trick is to control the environment.
If you’re used to leaving things lying around wherever you happen to drop them, it’s time to grow up and start putting your belongings where they belong. If it’s not meant to be chewed, put it out of reach (and preferably out of sight). After that, make sure Fido has access to plenty of safe chew toys.
Praise him when he chews on them, so he knows that those items are acceptable. If you want to take it one step further, teach him the “release” or “leave it” command, so that you can rescue any items he does manage to find. But never swap food for the object in his mouth; unless, that is, you want to teach him to go find one of your most treasured possessions any time he wants a treat.