We've found that a combination of these three mulches has done the best job of keeping the small local fauna out of our garden beds: Cedar mulch, pine mulch, and pine straw.
The cedar mulch is finely chopped and helps insulate the garden; it's the first deterrent for digging. The chunkier pine mulch is just for effect; we only use it in areas like the garden path. The pine straw goes on last, and seems to be the most important of the three (we've found it to be the most effective and easiest to work with) because little critters don't like walking on it—especially when coupled with the other mulches.
Best of all, the mulches and straw help to insulate the garden beds and keep weeds at bay too. While it sounds like a lot of work, it's quite easy to freshen up and add more as needed, and since these are locally-available from most gardening centers (many times made from recycled Christmas trees and the like), it's an especially green resource.
And they're not quite as mean-looking as the plastic fork method.
Have any other eco- and animal-friendly tips for keeping critters out of the garden? Do share!
(Image: Amber Byfield for Re-Nest.)