Commercial repellents work by creating an olfactory barrier to keep cats out of the area. For instance, the powder called Shake Away Cat Repellent has the fragrance of coyotes, foxes, and bobcats—predators that cats are afraid of.
Peel oranges, lemons, limes, and grapefruits and use them in your garden. Some people use mothballs or used coffee grounds; others use vinegar or eucalyptus.
Before planting, create physical barriers like chicken wire over the soil or mulch across the planting bed. Cats detest materials with bristles like chicken wire.
You can mulch with eggshells, stone mulch, holly clippings, or sharp-edged pine cones. Cats will be turned off by these harsh materials as they prefer to dig and poop in loose ground.
You can try squirting cats with a Super Soaker or similar water cannon when you find them in the restricted area. The idea that they belong outside of your planting bed is strengthened by this technique.
Compared to humans, cats can hear far more. Cat Stop is an electrical device designed to dissuade cats. It works by using a high frequency sound that is inaudible to humans but extremely annoying to cats. Installing is simple.
Put marbles or pebbles in an empty coffee can to create a noisy gadget that will ring when a cat steps on a fence. You may also use wind chimes or a sensitive bell that will ring when a cat shakes something.