I'd just like to note that separation anxiety is a popular misdiagnosis and that just chewing things up when left alone is not really an indicator of it. As the owner of a true SA dog, believe me when I tell you that when your dog has SA, you know :yikes:
Crate-training (or some other form of confinement) is an excellent way to break a dog of the habit of inappropriate chewing while you're not around to correct and redirect. As far as a dog is concerned, the entire world is a chew toy and unless they have extensive experience with only having access to and being permitted to chew on their own chew toys, most dogs will go ahead and explore the world with their mouths when left at liberty to do so. Crating does not have to be forever. Most dogs once they get a little older and out of their puppy and adolescent chewing phases, and once they have the extensive experience of ONLY having access to their own approved chew toys, can be "uncrate-trained and eventually left to have free roam of the house.