Bury chicken wire or plastic mesh along the bottom of the fence. This will create an underground barrier that your dog will be less likely to dig through.
Install a low concrete footing around the bottom of the fence. This will make it even more difficult for your dog to dig.
Pack dirt around the base of the fence. This will make it more difficult for your dog to get a good grip to dig.
Use a digging deterrent spray. These sprays can be applied to the fence and will make it unappealing to your dog.
Provide your dog with an alternative digging spot. This could be a sandbox, a dirt patch in the yard, or even a hole dug specifically for your dog.
Make sure your dog gets plenty of exercise. A tired dog is less likely to have the energy to dig.
Train your dog not to dig. If you catch your dog digging, immediately interrupt them and say a firm "No." Then, take them to their designated digging spot.
Don't punish your dog for digging. This will only make the problem worse.
With patience and consistency, you should be able to train your dog to stop digging out of the fence.