Dogs, from Porties to Westies to sharpei, like digging for plenty of reasons. The most significant cause must be the dog's hormones. A male attracted to a nearby female may try to bolt his high-fenced coop by tunneling. A female that in particular just had her first season may demonstrate a "nesting" behavior. Both types can be consulted with a vet, and reduced by neutering or spaying. But aside from their doggie make-up, the next likely explanation is that digging is really part and parcel of your pet's package. In this case, expect the dog to outgrow it if he is still a puppy.
But if your sharpei is an adult, if he developed the habit only recently, and if he only does his work in one specific spot, then something must have happened to trigger such a behavior. Try checking if there is some interesting object buried on that spot, or if some cute vermin have made their home there. But if there is nothing to see there, you may want to apply some deterrent spray where X marks the spot. Other examples of blocks to his access are a pile of stones, or a temporary wire netting fence.
If your dog is already an adult and it's an old, stubborn habit, you will be better off limiting the dog's preoccupations than stopping him altogether. After all, digging is a natural habit, through and through.
A more or less last resort would be to give the sharpei a small plot in the garden where it's alright for him to nose dirt about. Start by digging out all the plants, put in loose earth and sand, then bury a handful of doggie biscuits (that is, if your dog can eat soiled food). Let him watch you bury the item so he knows food is around. Praise him if he is successful. Fix up the area again every few days with biscuits, toys and bones and praise him whenever he finds the items. If you want to stop because he is letting go of digging, just put fewer and fewer treats until he doesn't bother digging. In any event, hiding attractive but injurious objects that will literally shock the habit out of the dog is absolutely no way to help him.
And what is the final, final last resort? Vigilance. Watch your sharpei whenever he is out back and distract him when he starts shoveling. Call him, shake toys and praise him to break the habit as soon as you can.