Cat Repellents
There are commercially available non-toxic dog and cat repellent sprays. Good products are scent-free and environmentally friendly. Citrus fruit peels (lemon, orange, and grapefruit) and tea leaves are thought to be natural cat repellents, though not everyone has success with these.

A Resident Dog Or Cat
An adopted pet can act as a security guard for the garden. If there is a resident dog or cat that has laid claim to the yard, it's far less likely that neighbourhood cats will visit, and a resident cat can be trained not to use the garden as a toilet.

Sound Devices
Ultrasonic sound devices that run on batteries can be used to drive dogs and cats from the yard. These motion-activated devices emit sounds that animals hate but that are inaudible to humans.

Strategies To Avoid
There are a number of cat-repellent strategies that are commonly recommended but shouldn't be used. For example, mothballs are toxic and although they are an effective pest repellent, they can be deadly for pets, local wildlife, and children who may pick them up and put them into their mouths. They will also repel beneficial insects such as ladybugs, which eat aphids and other garden pests.

Sprinkling hot pepper (black pepper, cayenne, etc.) is also a bad idea. Not only does the pepper have to be reapplied frequently, but there is the risk that animals will walk over it and then lick their paws or rub their eyes. Small children may also pick up the pepper on their hands and then put their hands in their mouths or touch their eyes.