Puppies should be told from day one, "no jumping." Anything you do not wish your cute little puppy to do when it is full-grown should not be allowed when it is a puppy. Think about the behaviors you allow your puppy to do; is it something you will always allow him to do even when he is full-grown? If the answer is no, do not allow your puppy to do it from day one.
When your dog has all four paws on the floor, give him attention and praise. If he jumps up at any point, freeze with your arms folded on your chest until he calms down. Instruct guests and all members of your household to consistently ignore jumping. If you have visitors who ignore the no-jumping rules, keep your dog on leash during the visit and gently remove him if he jumps. For anything your dog gets in life, whether it's your attention or a meal, only give the reward when all four paws are on the floor. Jumping up should end all attention and rewards, while remaining fixed on the ground garners all the pleasurable reinforcement a dog desires — treats, petting, play.
If a dog is stressed or afraid, their demeanor and typical behaviors will change. If you see this in your dog (or really any dog you know) you should step back and check on your dog. Are they hurt? Did a new dog come around they don’t know? Has the weather changed? Is it hot outside? When was the last time they had a chance to go outside to pee or poop?
I remember going to a dog park where a little 4-month-old Boxer puppy ran around jumping on everyone. The dog was not heavy enough to knock most of the adults down. However, it left everyone with muddy pants and the dog was big enough to knock over small children. The owner did nothing to stop the jumping puppy. After all, it was just a small pup. Everyone around her was pretty annoyed at the muddy prints the dog was leaving all over their clothes. That is an owner who will have a problem with her dog jumping on people when it gets older.
An anxious or playful pup may leap high quickly and suddenly “poke” at your face with their nose. That can be triggered by leaning over the top of them especially when they’re in a high-arousal situation like a homecoming or around other dogs. It may be a way for stressed pups to relieve their anxiety, so be aware of situations that cause these behaviors. Dogs control each others' movement with their body language. Think how a Border Collie makes sheep move just by getting close. You can stop your pup’s jumps by stepping close to him just before he leaps. Cross your arms and step into the pup’s personal space before he crouches to leap.
While the idea of "training" may seem daunting, it is simply teaching an animal what behavior works or doesn't work through resulting consequences — so whether you realize it or not, you are actually training your dog every moment of the day. Fortunately for you, preventing jumping is possible even without structured training. There are some simple solutions to this problem that require minimal effort and fit easily into your normal interactions with your dog.
When he gives up and stands still (staring at you like you’ve gone crazy), THAT’s when you greet your dog and give him some love and attention. This is the reward he was looking for. Following these rules will ensure he learns that he will only earn that reward by not jumping (don’t overdo the high-pitched voice saying, “GOOD BOYYYYY” or it will just rile your dog up even more to start jumping again).
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You shouldn’t stop this type of jumping. You need to diagnose your dog's issue and remedy that. If your dog is just stressed being in a new situation, you should calmly get them off of you, offer them a treat to calm them down, and have them sit politely beside you until their stress level has subsided (or take them somewhere else so that they can calm down if it is taking a while for them to calm down.) But most of all, please do not just ignore this behavior change.
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.