In our house, we're "dog people." Don't get me wrong; cats are cute and sweet and all that jazz, but I'm highly allergic and the neighborhood cats love to use our gardens as a litter box. Not cool. Here are three natural, safe, and locally available things we've used in all our garden areas to keep the cats (and critters) out.
Over the last year, we've had our share of community cat problems, and we think we've finally come across a method that works for all parties involved.
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.)

Sheex Bedding
What?!? The mulch is exactly what draws critters *to* my garden! Cats think it's a giant litter box and squirrels see it as perfect loose bedding to bury their treasures in! Using landscape rocks/gravel is the only thing that keeps them out around here :(
I think it may depend on the materials you use - she's using highly aromatic materials that may irritate and repel the animals.
We sprinkle pepper under our front deck as the neighbour's cat likes to use it as a litter box. It works well, but you do have to keep reapplying it.
I agree with Aimi; the neighborhood cats adore my mulch. But I have had luck with Cat Stop, from Gardener's Supply. It detects motion and emits a sound cats don't like (and we can't hear). I bought rechargeable batteries to minimize the impact. But it's still plastic and fairly ugly — so not the greenest option out there. It works though!
I am a "cat-lady" as they say, even though I secretly believe my boyfriend loves them more than I do. We recently started letting cats play in the backyard. Our cats aren't climbers (some cats climb, others hide) so we knew they wouldn't risk jumping the fence.
I knew they'd use the outdoors as their litter box (woohoo! less scooping for me) but I didn't think they would gravitate for my flower beds. Then I started spotting neighborhood cats in the beds, too. How did my daises bed become a feline bath house?
I didn't want to try anything chemical, so I went for mulch. No good, especially since one of the kitties is a long-haired fluff ball and came inside with the start of mulchy dreadlocks. My boy kitty is very curious and playful. He though the mulch was a great new toy.
I tried black pepper. It worked but washed away with the rain. Vinegar had the same effect. Eventually, I switched to cayenne pepper. In an effort to make it stay, I bought new weed matting, mixed 1 tbsp CP in a water bottle. I sprayed the matting with the concoction and left it out to dry for several days. Then I put it in the beds. Three months later, the cats still avoid it. I don't know if the smell is still there or if they've just been conditioned to stay away, but so far, so good.