3. Because they have been rewarded for this behavior in the past, whether purposely or unknowingly. Some owners may, at one point or another, allowed the dog to jump on them or on their furniture, welcoming their dog's enthusiasm to see them. Other owners inadvertently reward their dogs jumping, simply by doing something good--such as walking or feeding the dog--right after the dog has jumped. Even if they told off the dog for jumping, by providing the dog with a walk or with food, they make the dog connect these positive actions, with a not-so-positive action: jumping! The dog sees thing in a very simple, linear fashion: if he jumps, he'll get to go for a walk--or even better, he'll get fed!
By playing some simple games like fetch with your dog, you can kill 2 birds with one stone. First is that the actual playing of the game will surely tire them out so much that they won’t have the energy to jump the fence. Second is that you are associating the fun of the game with the yard. If they have fond memories of the yard they will be less likely to try and get out.
Teach your puppy a conflicting behavior such as “fetch your ball.” She can’t jump up if she’s running to bring you her ball or favorite toy. Just the name of a special game or toy—“go get your bear!”—can change the dog’s focus and redirect the behavior long enough for you to evade the jumping. With enough repetition, your puppy will begin to associate your home-coming with “go fetch” instead of jumping up.
A conflicting behavior when you come home—like “sit”—helps enormously. You’ll need to practice your puppy’s “sit” during calm moments first, and then ask for this polite behavior before you leave and when you arrive home. Guests will appreciate a polite “sit” when they arrive, too, as they won’t appreciate your puppy leaping around and mugging them for attention.
Unless given a command to jump, a dog should never be allowed to jump on humans. A dog that jumps on humans of its own free will is a dog that does not respect the person it is jumping on. Even those cute little toy dogs should not be allowed to jump on people. While you may think it is cute, it is not cute to everyone else. Not only is it annoying to most people to have someone else's dog jump on them, it can also be dangerous. A jumping dog can knock people over, muddy their clothes, put runners in nylons and scratch the skin.