I watched this decorating show there they did this backyard and had a digging spot for the dog to dig in as it was a digger too.
Suggestion the decorator made was bury toys in the sand so that it has something to hunt for. They don't want to just dig sand and nothing at the bottom. they need to find things.

Our dogs are lucky as they have 2 acres to run in and bush to dig and do what they like, they can be all dog on our property.

Dogs dog bored and some dig to get out and get somewhere, to do something. You got to keep dogs busy.

Also when he digs where he's not too, tell him LEAVE IT and take him over to his sand box and start digging yourself. before you take him outside, bury things for him to find and enjoy, he will love it so much.

WE tell our dogs to LEAVE IT if they do start digging in the garden after something they smell. WE did that since they were little puppies as our puppy trainer told us that one. It works too.