There are many reasons that can cause a dog to be destructive such as boredom, attention seeking, teething, adolescence, lack of stimulation or separation. The symptoms can be various, such as chewing things that they shouldn't, digging, scratching at doors and walls or ripping of carpets. Ensuring your dog is well exercised, mentally stimulated and has a good diet can help to alleviate destructive behaviour. Provision of plenty of allowed chew items that are rewarding for the dog to chew is another positive step to teaching your dog more appropriate chewing habits.
If your dog's chewing behaviour is excessive or coupled with stress behaviours and/or barking/howling then we strongly reccomend that you seek advice from a suitably qualified behaviour specialist - ask your vet for a referral to a local behaviourist.