A New Nightwatchman?

My morning visit to the raised beds today revealed evidence of a very busy night in the garden.  No plants had disappeared; no leaves had been chewed; the soil was undisturbed save for a moderate hole in the corner of Bed 1.  But Somebody had dug mysterious moats all around the outside of the beds, right up against the boards.  We're talking a good 48 lineal feet of trench, up to 4" deep.  Pretty impressive digging.

I immediately assumed that Somebody had been trying to break into the beds from below.  Voles?  Moles?  Rats?  Having bragged to my older brother just last week about our inexplicably mole-free neighborhood, I feared divine retribution for my boasting.  Reason quickly dismissed this theory, however.  Whoever dug these trenches is obviously a champion earthmover.  S/He would not have needed to try every inch of the perimeter in order to get into the beds.  Besides, the soil surface was totally accessible (and a lot softer than the clay pan upon which our garden rests). 

So what would Somebody be after at the outside edge of our beds, where the nipplewort thrives in defiance of my attempts to suffocate it with wood chips? 

It seems too good to be true, but I suspect that my garden has been blessed with a nocturnal slug snacker. 

Our backyard is a known hideout for raccoons and possums, and although I've never seen them, the neighborhood definitely harbors at least one skunk.  Could we have a backyard skunk??  The imagination thrills!  The imagination also suggests that we start keeping the cat in after dark. 

At any rate, even if this Somebody is also the culprit who filched a whole baby Bibb lettuce the other night (which, come to think of it, was pretty slug-infested..), it is a small price to pay for such an industrious pest-removal specialist.  It will be interesting to see if my slug beer-traps start going unused...