This seems to work, and costs nothing.
I came home at about 4pm and found a pile of dirt on the edge of the lawn right in front of the porch. I said a few words aloud, pushed it down with my foot and went in to change clothes and check the forum.
When I went back out a second pile of dirt/hole was 2' from the first
so now I was really annoyed. I pushed it down with my foot, then got my sharpest shovel, and sat on the porch steps and watched. Sure enough, within about 15 minutes the grass started to vibrate violently between the two previous mounds, the stopped. I very quietly stood up, and held the shovel in position. Next time the grass moved I jabbed violently over and
over. It's been nearly 24 hours and no sign of further activity.
(No, I'm not going to dig up the lawn to verify my results)