You could also try training the dog to dig in a spot that is ok to do so. (like a sand box) dogs like to dig! If you catch them digging, scold then direct them to the spot they are allowed to dig and encourage it only in that place they will understand a bit easier. Sometimes dogs that are a bit obsessed with digging it is easier to enourage digging in one spot then to be po'd at them all the time and frustrated with doggie landscaping skills lol!
I agree with the poop in the hole trick works well most of the time.