No matter how much you adore your pet, they can still get destructive while you are away. If your couches and chairs were the first to go, other furniture will soon follow. Attempting to "train this behavior out of them" is a losing (and frustrating) battle. Understanding the root cause of this behavior is the key to letting your pet roam free while you are away.
It is important to understand that your dog does not act out of hatred or vengence when you leave for the grocery store. They are merely exercising their "ownership" of the house, the couch, or other such item they destroy. In some cases, their anxiety about your departure or arrival will cause them to chew relentlessly. Here are a couple of tips to stop this behavior completely no matter how out of hand it already is.
First, be persistent. Consistency in your act gives your pet a basis for behavior. Through your everyday body language you are setting the ground rules for their behavior in YOUR house. Stand up tall, walk firmly, "own" the place. Don't get excited before you leave and be sure to remain calm when you get home. Coming and going is a common occurrence for most people. By exerting a disinterested attitude about it your pet won't feel as much anxiety around the event.
Second, realize that you are the head of your house. You are the pack leader. It is important that you ALLOW your dog to enter and exit the house at your command. If they are leaving or entering with you, make sure you (not your pet) do so first. Remember, YOU lead the pack, YOU set the standards, and YOU own your house-and your pet wants this! Let them follow you and they'll be much more at ease.
Finally, never allow your pet to jump on your furniture without an invitation. If they are tearing up a couch while you are away, make it off-limits until this destructive behavior stops. Just as the house is yours, so is everything in it. Deciding how your pet can use your furniture vs. the other way around is a solid step toward preventing that furniture's destruction.
By simply applying these lessons consistently with your dog, you should see great results. It may take a few weeks, but once they understand who's house they live in and (most importantly) that it is not their own, you'll feel much better about hitting the gym and letting your beloved pet roam free.