It is my understanding that the digging behavior you are experiencing with your wolf hybrid(s) is different from the digging that a dog owner would experience. The denning instinct is much stronger, less buried by thousands of years of domestication.
I don't know if there is anything you can do about it. This might be one of those behaviors that you just have to kind of shrug your shoulders and accept if you're going to keep wolf hybrids in your back yard. Be prepared to install some sort of in-ground barrier to keep them from digging under the fence (if you haven't already). The one person I know who keeps high content hybrids installed hog fence underneath her fence line, and extended the fence up to 8 feet in height and then had a lip installed the discourage climbing over. But she lives in the boonies, out int he middle of nowhere, and didn't have neighbors complaining about her prison-like yard.
I suppose you could only have them out in the yard when you are physically standing right there, ready to disrupt and distract when they start to dig?
What kind of containment area do you have them in? If it is a separate place, secure from the rest of your yard, you could always sacrifice it to the digging? Our dogs have their own yard, but I don't need any special containment for them other than the regular fence.