Chewing is a natural behavior for your dog, but coming home to find your couch strewn throughout your living room is not desirable for anyone, you or your dog. Dogs need to chew when they are young, as a way to relieve the pain of teething, and older dogs chew to loosen debris from their teeth and keep their jaws and teeth strong and healthy. Therefore, you do not want to teach your dog not to chew, just not to chew on your furniture!
Besides not wanting your furniture or other possessions damaged, chewing on furniture can be dangerous to your dog, as they can damage their teeth on hardwood or sharp corners, ingest furniture polish, loose bits of furniture, or upholstery, or they can damage their mouth with slivers. Besides being expensive to replace damaged items, you could incur veterinary bills if your dog is injured or made sick by ingesting something non-digestible.
Because dogs need to chew, any method used to prevent them chewing on furniture should provide an alternative safe chewing opportunity. Providing a viable alternative to their furniture chewing habit is vital to success, and your dog's health and happiness. It is easier to train your dog from an early age to chew on appropriate items before they get into the habit of damaging your furniture, by providing appropriate chew toys and items. If your dog has started chewing furniture you will need to break that habit, as well as redirect them to appropriate chew items.