There are a lot of cats in our neighbourhood, so when we first installed our sandbox we decided we needed some kind of way to keep them from using it as a litter box.
I made vertical curtains to keep the cats out, which worked extremely well for quite a few years. But then, being outside, the fabric started to wear out.
We have this one neighbour down the street who irritatingly allows his dog off leash all the time. Checkers likes to visit all of the backyards and we've had our run-ins with this neighbour because we don't enjoy cleaning up the presents left behind, I don't enjoy nearly running over the dog when it darts behind my car unexpectedly while I'm backing out of the driveway, and the dog has occasionally been aggressive towards the kids (once knocking Elizabeth off her bike). The relationship has been improving though as he's made a small effort to keep the dog out of our yard and also to help the kids make friends with the dog.
In any case, on this particular day in the spring last year Checkers was running loose (again) and his dog friend Molly from across the street was chasing him. And the dogs ran right through the now-flimsy curtain in the sandbox. The neighbours did offer to replace it but I figured it had needed replacement anyway so I turned them down. And then didn't replace the curtain. We actually got away with this for quite a number of months, but eventually a cat started to poop in the sandbox and we stopped letting the kids play in it and I decided I really ought to make curtains. Daddy was convinced the culprit was "our" cat and we even stopped giving it food treats, which some of us were sad about.
Anyway, one thing led to another, and winter came and I thought well, maybe it's silly to put curtains up right before winter. So that particular chore got put off. And put off some more. And the cat kept pooping in the sandbox, and I kept getting more and more creative with putting bits of wood and netting over the sand to keep the cat out and spent much quality time sifting the frozen sand etc until it finally snowed and that seemed to stop the cat.
Then spring came, and I hoped the cat would not come back. But it did. So I buckled down and made the curtains. By the time I did it was June and I was pregnant and therefore banned from dealing with litterboxes so Daddy had to take over the cleanup duties. He sifted out all the cat poop and he bleached the sand and combed it flat and we were pretty happy to think we'd finally have the sandbox back in use...
The very next morning we noticed that the sand had been disturbed AGAIN. Despite the curtains. I looked at the footprints left in the sand and realized I had been fighting against a racoon (not a cat!).
So Daddy built us a very sturdy wooden cover and then he sifted and bleached the sand again. And now we have a sandbox again.