When your dog jumps the fence, it can be for a number of different reasons. Most of the time, it's just because they want to be somewhere else besides home for a while. But, they can also escape because their needs aren't being met somehow. Some dogs will wander to look for food or water if they're not getting what they need at home. They will also wander to go look for a mate, especially if they happen to smell a female close by that is in heat.
Fortunately, there are a few different solutions that you can try.
If your dog is climbing over your fence, you can always make an L-topper. This is basically wire that is attached to the top of your fence in an upside down “L” shape, so they physically cannot climb over the fence anymore. Learn more about L-toppers and footers (that we talk about below) by checking out this page on DoggyBakery.
You can use this same solution at the bottom of your fence to stop your dog from digging underneath it. It's not expensive to implement, either. You should be able to get the wire for it from a local farm and tractor supply store and the hardware necessary to attach it to your fence.