A friend of mine has some critter on the loose in her yard that's making tunnels, and is resistant to being persuaded to leave the premises. While I have critter problems, all of mine are above-ground dwellers, so I don't have experience from which to offer her advice and I'm hoping some Green Girls followers out there can help her. So it is a mole, vole, or other? And what methods have you used to get these varmints to move on?
 
She offers some clues:
 
1. The holes are under a crab apple tree, about 3 feet apart and a good 8 inches deep.
2. The tunnel is horizontal. You could run the tape measure through the hole and it would pop out the other side
3. She has dug up the tunnels, washed them out with water, smoked them, placed planters over the tunnel holes for several years in a row. She keeps them there long enough (a month or more?) to encourage it to move on. And it seems to move, until the holes re-appear late spring. Ugh!
 
What pesky animal makes these holes and how does she make them realize they've worn out their welcome?