1 handful lemon peel
1 handful coffee grounds
If the neighborhood cat has mistaken your garden for a litter box, lemon peels will make the area a lot less inviting. Use a food processor to chop up a handful of peels and then mix them with your leftover coffee grounds. Scatter the mixture along the border of your garden and work it into the soil with a hand trowel. Cats simply hate the smell of citrus and should steer clear. If your indoor plants are falling victim to your cats, this method should work for them as well.
This is included in Pest Control only because cats, while being pets, can sometimes be pests.