Short of putting your dog on a chain, you may think you have done everything in your power to prevent them from digging underneath your fence to freedom. Some dogs are determined to get out no matter what you do. Male dogs can smell female dogs close by and it can make them crazy to escape. Some dogs just can't stand to be enclosed because their natural urge to roam is overpowering.
While you know that you are keeping your dog inside an enclosed fenced area for their own safety, the dog does not. When they continue to dig their way underneath your fence, you might not think there is nothing left you haven't tried to stop it. However, there is invisible fencing that could fix everything.
Many dog owners that have no fence will invest in invisible fencing because they can't have a fence in the area where they live. Some use them just because they don't want a fence enclosing their property. The main reason most dog owners use invisible fencing is because it works!
There are two types of electric invisible fencing for dogs and I found all of the information I needed by visiting https://www.doggybakery.org/ and a few other places. You can use either an in ground wired invisible fence or one that uses no wiring at all! They are not difficult to install and either version will work perfectly with your existing fence to help deter your dog from digging their way to freedom!