When you have a flock of sheep and it is your livelihood, the last thing you need is for one of your sheep to escape by jumping over a fence. To stop a sheep from jumping a fence, you have to imprint a negative experience in its memory. It works the same way with all animals, including dogs. The sheep needs to associate a bad experience with its attempts, or success, in jumping the fence in order to stop the behaviour.
Use herding dogs that will shepherd the sheep away from the fence. If the dogs do not stop the sheep jumping over the fence, use barbed or electric wiring.
Nail barbed wire to the top of the fence surrounding a flock of sheep. Place it at least shoulder height to make it difficult for the sheep to jump over. Observe the sheep to determine how high the sheep can normally jump and place the wire at a greater height, if necessary.
Use electric fencing if the barbed wire did not alleviate the problem. Follow the instructions of the electric fencing's manufacturer for installation and supplying it with electricity. Some electric wire is charged with a battery; other types require plugging into a main electrical supply. Electric fences are inexpensive and come with fibreglass poles that can be pushed into the ground anywhere you need a fence.
Train the sheep to keep away from the electric wires and to avoid running into the fence. Let the sheep touch the wiring, giving it a small electric shock. Over time, the memory of the shock will imprint a negative experience in the sheep's mind and it will not jump against or over it.
Keep more than one dog in the field with the sheep to better work the sheep and keep them under control.
Ask a friend to come and help you install the barbed wires and the electric fencing. You may be shocked by electricity and need someone to switch the electricity in this case. Ask an electrician to help you install and check the wiring if you are not an expert.