1st Answer:
either get a taller fence or an electric collar
2nd Answer:
There are also available anti jumping harnesses at the larger
pet shops or through the doggy catalogs. They restrict your dog
from jumping and you can safely leave them on your dog. I would
recommend this over an electric collar. With that you would have to
stand there all day long to zap your dog when he decides to jump
the fence. That would be very inconvenient for you