Dogs usually chew for two reasons: they're teething or their bored. Teething usually begins at four or six months and could last two or three months, depending on the breed and size of your full-grown puppy. Most chewing, however is the latter, and puppies do not outgrow boredom destruction.
The number of toys that you purchase is important, but not as important as the TYPE of toys you buy. Dogs like toys that taste good or reward them for chewing. Good toys for encouraging proper chewing are: hard rubber toys (i.e. Kongs (TM)), cow hooves (not pig ears!) Nylabones (TM), compressed rawhide, floss toys or ropes.
All meat and fish bones, they can cause choking and intestinal damage. Toys that contain small hard parts, such as squeakers, hard pieces are dangerous if swallowed. Old clothing or household items, your dog can't distinguish new shoes from old ones he's been allowed to chew on. Be very careful with rawhide, which is why I suggested, compressed and even that can be dangerous if your dog is an aggressive chewer. Rawhide is dangerous if your dog gobbles it down. Digestive problems can occur if large pieces are swallowed.
Note: you should always monitor your dog when giving him/her a new chew toy. If a toy is broken into big chunks that can be swallowed, it is best that you do NOT give that toy to your dog. Toys can cause choking hazards with aggressive chewers. Use your best judgment and follow the package directions.
As you probably already know, your dog will not stop chewing if you give him/her no toys to chew on. The furniture or landscaping can testify to that. If you follow the steps to proper chewing, you will be able to rely on your dog to target only his/her toys. Chewing on toys can also discourage other bad behaviors such as digging or barking.
Teaching proper chewing:
Obtain good chew toys. If you your dog is not interested in them but is a chewer, use a bit of peanut butter or bacon grease to stimulate interest. Praise your dog for chewing on his or her toys. Keep all toys in a central location that is easily accessible at all times. A large milk crate or cookie tin can be used to contain all toys. Watch your dog. (For a destructive dog, keep him or her tied to you on an indestructible leash). When he or she looks around for something to chew, say, "Do you want a toy? Let's get a toy! Walk them to the "toy basket" and dig around inside to generate interest while saying "Get a toy! Do you want a toy?" When your dog retrieves a toy from the basket, praise your dog. If he or she picks up the toy but then drops it, continue generating interest in the toys. Keep in mind that if you have something you think is good, your dog will want it as well. Continue to do this until you see your dog going to the basket without any prompting. Be prepared and praise your dog! If you must leave your dog alone and he or she is not reliably going to the basket, do not leave your dog loose in the house. If crating or confinement is not an option, make sure that you treat all areas with pet deterrent (like Bitter Apple(TM)) to discourage destructive chewing while you are gone.
When you see your dog pick up an inappropriate object, firmly correct him by saying, "Leave It". Take the object from him, praising him when he gives it to you. Give him one of his toys and praise him when he takes it. If your dog runs away with the inappropriate object DO NOT chase him or her. Most dogs love to engage in the chase game which consists of the dog buzzing by you with the item in it's mouth and running all over the house frustrating you even further. Making the inappropriate object even more fun for your dog. The solution is twofold - first, never chase your dog for the item he or she has. Second, try trading your dog for the item get a ball or chew toy or even treat and entice your dog to come to you with or without the other item. Ask for a sit, and then place your foot on the dropped item. Throw or give the ball to your dog.
Do not try to correct or punish your dog unless you catch him in the act! He will not understand.
Confine your dog to a chew-proof area whenever you can't watch him. Leave him one toy to chew on. A dog crate is the safest place for your dog when he is unsupervised. If you opt to confine your pet to a small room, spray furniture cabinets with Bitter Apple (TM). Be sure electrical cords are inaccessible or unplugged.
Exercise your dog, especially before leaving him alone. If he's tired, he'll sleep instead of chewing.
Give your dog unsupervised freedom gradually. Check on him after five or ten minutes initially, leaving him slightly longer each time he has done no damage. Many puppies aren't trustworthy the first year so don't be discouraged.
Do not assume that, since you bought all these toys your dog will chew on them. You must teach your dog what you want. Spend the time following this method and you can eliminate chewing problems quickly and easily.
It would be best for you to not leave your dog unattended in the yard during the day. However, for some people this is not an option. Make sure you treat the areas that get chewed with a deterrent or barricade them from being accessible to your dog. In extreme cases you could use fencing designed to keep dogs in or out of an area. Always leave your dog plenty of toys to chew on (one or two will NOT be enough). The more toys your dog has that he/she likes, the less likely he/she will be to destroy your things.
It is also a good idea to rotate toys. If they have ten toys to chew on, hide two of them for two weeks and bring them out again in two weeks and rather then buying new toys regularly. It can be a whole new surprise when the old toy comes back out. It gives the dog some variety without constantly buying new toys.