4. Use the "Sit" command. This is one of the most basic, and important, commands. As such, if your dog is well trained, he will respond to the Sit command before even thinking to jump. If he does not respond well to the Sit command, then more training is necessary, as this is the foundation for dog obedience training. Train him until he responds to it in everyday situations, such as greeting and going for walks. The better he understands the Sit command, the much less likely he is to ever jump at all.
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.
Remember, Jumping up can be dangerous as well as annoying. Just as many owners are sued for their jumping dogs as their biting dogs. Young children and elderly people can easily be toppled over and seriously injured by exuberant, friendly dogs. Start now to teach your puppy not to jump up. Even little dogs can cause problems and injury to themselves and others when they jump up.
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.
When a dog jumps on a human of its own free will, it is not "greeting" the human, it is asserting its dominance over the human; it is the dog communicating that it is alpha and/or wishes to own/control the human. A subordinate would never dream of running over and jumping on the alpha dog of the pack. Space is respect and lower members of the pack respect the higher members. If your dog jumps on humans, it does not respect them. Note: when a young puppy jumps on humans it is sometimes its attempt to reach one's face. Puppies need to be taught not to jump up on humans as this behavior will manifest into other meanings as the puppy grows up into an adult dog.