Dogs usually dig when they get bored. Talking your dog for a walk is one of the things you can do to stop him from digging. When his attention is diverted somewhere else, he'll be able to forget about digging.
Getting a sandbox where he can dig is also a wonderful idea. You can even plant stuff in the sand. You can put grass or even hide a bone to surprise your dog so he can be accustomed to digging only on that specific place.
It'll also be great if you put a fence around the area where you don't want your dog to dig. It doesn't have to be an expensive fence, just something to keep him from wandering around those areas.
You also have to observe your dog. When he digs in the 'off-limits' area, you have to go there rightaway and correct his behavior. Hold his paw and say "Stop!" then redirect him to the place where he can dig.
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I hope this information helps.