There are lots of resources available to help you cat-proof your yard. Many people find citrus peels, black pepper, garlic, citronella oil and blood meal help repel cats, but they need to be re-applied on a regular basis. Make a simple herbal spray using a handful of rue, (Ruta graveolens) boiled in a litre of water for ten minutes and allowed to stand for 8 hours. Strain the mixture through a piece of muslin or stocking into a spray bottle and spray around the areas where the cat frequents your garden. This may need to be repeated twice daily for up to a week to ensure cats do not return. The smell of Rue is offensive to cats and it may give them the message that there is already a dominant cat on the premises. If you don’t have access to rue, you can make a mixture of 2 cups vinegar, two cups warm water, and 10 drops of one or more cat-repellent essential oils (lavender, citrus, citronella, cinnamon, eucalyptus and mustard). Pour into a spray bottle and spray the problem area thoroughly.
You can also plant rue, lavender, pennyroyal, Coleus canina and lemon thyme, all of which are unappealing to cats. If you find that a cat digs in a specific area of your garden at night, water this section just before dark. Cats do not like to have wet, muddy feet. Motion-activated sprinklers can also help to keep cats away, but watch for over-watering. Cat-proof fencing is an option too, since it serves to keep cats out as well as in. There are also a variety of ultrasonic cat deterrents available, which use a harmless burst of ultrasonic sound to keep cats out of the area. These deterrents also sometimes work on other mammals such as raccoons.