Digging is a normal, natural dog behaviour. There are many reasons why dogs dig. It's fun, they are bored, they are hunting, some breeds are genetically programmed to dig (like terriers), to escape or to stay cool. Your first step in solving a digging problem is to understand why the dog is digging.
Choose an area in your yard where you won't mind your dog digging and follow the instructions on how to make a digging pit. Fill in the existing holes when the dog can't see you and top off the hole with fresh dog poop. Dogs hate to get their paws soiled with feces.
Increase his exercise. Rotate his outdoor toys so they retain his interest longer. Spend more time playing and training him in the yard where he digs.
Hire an exterminator.
Choose an area in your yard where you won't mind your dog digging and follow the instructions on how to make a digging pit.
This means your dog finds it more rewarding to be out of your yard than in it. Fortify the fence so he can’t escape. This may include burying chicken wire underground so the dog cannot dig through to escape. Then, follow the suggestions for your dog’s boredom to make your home much more interesting and appealing to your dog.
Purchase a hose mister and/or wading pool to help keep him stay cool.
How to make a digging pit:
Step 1: Choose an area in your yard where you won’t mind your dog digging.
Step 2: Create a “dig pit” for your dog. Dig up the area and fill it with sand. Hide some durable dog toys in there.
Step 3: Encourage your dog to dig in his dig pit. Praise him when he digs in there.
Step 4: If you catch your dog digging in another part of your yard, redirect him to his dig pit and praise him when he digs there, instead.
You can also have the dogs nails cut short. This will make digging in areas other than soft sand far less pleasurable and make him far less likely to dig outside his digging pit and keep in mind that most of the time dogs will dig when you are not present. So it would be a good idea to supervise your dog's outdoor time until he consistently uses his digging pit.