How to stop a dog from digging

So you have a digging dog and you're wondering how to get him (or her) to stop.
Well, I'm of the mindset that you don't — and shouldn't — stop him.
"That's ridiculous," you're all saying right about now. "I can't have him digging up my garden beds every time I let him outside."
I agree that he shouldn't be digging up your garden beds, or digging anywhere you don't want him to. But stopping the digging all together is, in most cases, just not going to work. Not 100 percent.
Fortunately, there's a way to manage to this behavior that will keep your yard and gardens free of holes, and make your a dog a happy little digger in the process too.

Why do dogs dig?
Digging is something we developed many breeds of dogs to do. Terriers are the most notorious diggers. They have been born and bred for centuries to dig up varmint. That urge to dig remains present among many of our dogs, terriers and mutts and all dogs alike. For many, digging becomes an enjoyable, rewarding and sought-after activity. Add in that inherent urge and that's why it can be so darn difficult to get a dog to stop digging.

The tank theory
This idea comes from my favorite author, Jean Donaldson, in her book Culture Clash. I don't have it word for word, but here's the general idea, anyhow: 
Essentially, she says to think of a dog as a machine with a bunch of tanks full of gas. Let's say that one tank is marked "chewing," another is "chasing," another might be "tug of war" and perhaps yet another is "digging."
Each day, these tanks need to be drained. If not, when a new day begins and more gas gets poured into the tanks — as happens every day, regardless — there is no where for that gas to go. It overflows.
So, the tanks represent doggie behaviors that the dog is instinctively inclined to perform everyday.
When a dog engages in those behaviors, the tank is drained. The dog's need for that area is met for that day.
When a dog does not get his tanks drained, the resulting overflow equals behavior problems. He's bursting at the seams, right?
That is where all kinds of behavior problems can develop. Maybe the dog develops a neurotic fixation for something like chasing his tail to try to expend some of that energy and drain his tank.
Maybe he claws at the door handle until it pops open so he can go outside and run.
Or maybe he chews incessantly at his paws until his hair starts falling out because he's bored.
And if he's a determined digger, perhaps he learns to dig at your carpet corners or couch or comforter or just waits until you look away for a moment to dig up your garden.
It's hard to say what the dog's brain will come up with when its hard-wired needs are not being met. The possibilities are endless.

Drain that tank!
For the reason listed above, I do not buy into the theory that we should stop our dogs from engaging in behaviors they are hard-wired to do simply because it inconveniences us.
Instead, you teach the dog to funnel that behavior into something that does not inconvenience you.
I'm all about turning unwanted behaviors into wanted behaviors, regardless of whether it's a hard-wired behavior or just any ol' behavior you don't like.
For instance, Sensi used to bark and bark and bark at pool sticks, and try to grab them, whenever a person made a shot on the pool table. The sound of pool balls hitting each other just sent him into a tizzy.
He was not responding to "no."
My solution? Train him to play pool. Suddenly, it went from "no one wants to play pool when Sensi's around" to "people are coming over because they want to play pool with Sensi."

The digging solution
Digging is one of the easiest problems to start managing.
Step one: Get a sandbox, fill with sand
Step two: Bury a toy in it
Step three: Encourage your dog to dig up the toy, praise him for doing so
Step four: Verbally reprimand the dog ("No! Bad dog!") whenever you see him digging somewhere that is the not sandbox, then immediately lead the dog to the sandbox and encourage him to continue his digging there.
Optional Step five: Reward digs in the right place. Some dogs might need a little treat to solidify for them that digging in the sandbox is the right place to dig. For other dogs, the digging alone may be reward enough.  
This is essentially the same training method as used with chew-training. Even people who don't know a whole lot about dogs seem to have heard about the "When your puppy chews something of yours, take it out of his mouth and insert or encourage him to chew on a dog toy instead."
Same thing, different behavior.
The biggest reward, of course, is that a tank is being drained every time the dog gets to dig in his sandbox. Every tank drained is a behavior problem averted, so drain those tanks!