Occassionally, the dog in the yard next door will dig one up, so I know it is actually moles, that are doing the damage.
I've tried the little wind driven decorator devices that make the ground clatter, I've tried pouring clorox down their holes. I've tried eradicating any worm and bug problem, I may have, hoping to remove any mole food source. . .All to no avail. This has been going on for several years now!
Myrl Jeffcoat http://www.myrljeffcoat.com