The book: "The Other End of the Leash" by Patricia McConnell has a section on this. Or (my memory is pretty bad), it might be in "The Rosetta Bone" by Cheryl Smith. When I finally decide to take lunch, I'll check and let you know.
If I recall, their suggestion is to 1) make sure the dog isn't digging out of lack of stimulation, and 2) give the dog an alternative. Some dogs simply love to dig, so the alternative is to give them a "sand pit" where they are allowed to dig. In other words, for a dog that simply loves to dig, you aren't going to break them of digging but you can break them of digging random spots all over the place. By designating an area where digging is allowed, you both solve your yard issue and you allow the dog to stimulate themselves through digging.
RATCHX3 High Jinks vom Neuanfang - Gotchya Day: 1/23/2013 DN, SG, SR, CA
Inspire Spark to Ignition! (Ignite) Gotchya Day: 10/8/2016
C-ATCH Pimg - RATO, UJJ (x2), DJX, HIT, CA, CGC, High in Games, Reserve High in Standard- CPE Nationals 2014