We've just never had this happen before - and we've been in the same place since 1995.
Two years ago they discovered a gap under the front stairs, but as soon as we see them digging through the dirt, we are able to deal with that.
For this, I dunno. I think we'll leave it a bit to see if we actually see any... then decide if we have to do something. They are freshly dug holes, though.

