There are many cat deterrents methods out there, from laying chicken wire before planting your garden (if you anticipate a cat problem) to adopting a dog, which may wreak more havoc than the cats. The best methods are the smelliest ones. Cats are notoriously finicky, and if your flower bed smells offensive, you're likely to be rid of them for good. Every cat is different, so you'll likely have to try several odor deterrents.
Sprinkle citrus fruit peels throughout your garden. Peel grapefruits, lemons and/or oranges and evenly distribute them throughout your garden.
Bury ammonia. Collect enough baby food jars to distribute at reasonable intervals throughout your garden. Fill each jar with one part ammonia and one part water. Then bury the lid-less jars up to their rims throughout your garden. Remove the jars from your garden once the cats have been gone for a week.
Spread blood meal fertilizer. Blood meal has a pungent odor that is offensive to cats and humans alike. Sprinkle a layer of blood meal fertilizer throughout your garden and allow it to rest on top of the soil. Do not turn it. If cats do not show up for a week, gently turn the soil with a spade to reduce the smell.
Apply commercial cat repellent. Commercial cat repellents come in powder or spray form and contain the urine of predators such as coyotes, foxes and bobcats. Read the ingredients before you apply it to make sure that it doesn't contain toxic ingredients. Apply the commercial cat repellent to your garden according to the manufacturer's instructions.