When dogs are young, usually under a year old, it's fairly normal for them to engage in significant chewing. Beyond this age, and usually at about six months, puppies can begin to be taught how not to chew on everything in sight. This an important behavior to teach for the safety of any items in home people hold dear, and also for the sake of the dog, who could accidentally chew or choke on dangerous items.
Dog chewing may continue well after the first year for a variety of reasons — usually boredom or a lack of exercise. Tired dogs don’t chew, so it’s important to make sure a dog has adequate exercise each day. A couple hours of walking, or an hour in the dog park may be a terrific way to cut down on chewing behavior, because the dog will typically prefer to sleep at home instead of attacking a shoe or a couch to relieve boredom and excess energy.
The real key to stop your dog from chewing, in addition to getting the dog plenty of exercise, is to provide constant supervision. It can be assumed that a dog wandering away from its owner is likely to find something to chew on. Keep the dog on a leash when out, and keep a close eye on the dog when at home. This gives owners the chance to provide quick correction if the dog begins to chew on anything.
Corrections can be varied. They can include a quick snap of the leash and the word “No!” Alternately, dogs may hate the sound of pennies in a can and the can may be shaken each time chewing begins. Some people prefer a squirt of water aimed at the dog. Unacceptable corrections include screaming at the dog or hitting it, as this may stress the dog into more chewing behavior.
The other half of this equation is giving the dog acceptable things to chew. Have a few designated chewing toys, which should never be old clothes, shoes or anything formerly belonging to the owner. Any time chewing behavior occurs, perform the correction, give the dog the designated toy, and if the dog takes it, also treat the dog or give praise. This way, a dog can quickly learn that there is a difference in the home between acceptable and unacceptable chewing items.
It can take a few months to completely eliminate dog chewing, and it is wise to have a space for a dog that is safe when the owner can’t watch it. Crates are excellent for this purpose, and also bear in mind that it’s dangerous for the dog to be in areas of the home where it could chew on anything that is unsafe. Make sure to get things like electrical wiring off the floor, and try not to leave socks or shoes around that the dog might find attractive. Outdoors, be sure any plants that might be chewed are non-toxic, since poisoning can be a concern.
Usually, with attention, correction, substitution, and exercise, most dogs will end chewing behavior. If it continues, consider consulting a dog trainer or dog behaviorist for more tips. Most people can resolve these bad habits with a little time and attention, however.