Bobert, I hadn't really considered voles, as I am in a small town on a residential sidestreet.
Howsumever I HAVE seen holes of the size you describe. Moles occured to me, but they are not supposed to be that destructive to plants; they are just supposed to eat the livestock they come across as they tunnel. No hills, just the occasional hole a mite too large to be an ant hole, and now the Peruvian daffs are gone, too.
grrr. Diatomaceous earth works great on the slugs.
There is nothing natural about cultivating a garden, and nobody promised us no work.
I would not call mya garden large, but I DID mulch outt all the grass and do flowers ...