Some ways to scare cats away from a yard or lawn include motion-activated sprinklers, guard dogs and ultrasonic devices. Simply shooing cats away can also be effective, as most feral cats quickly flee when humans walk directly towards them. Making strong eye contact and using a loud, deep voice achieves the best results.
Motion-activated sprinklers are sometimes costly to install, but they are a very effective option. Sprinklers take advantage of cats' natural tendency to avoid water. However, water can be harmful to cats if outdoor temperatures are exceedingly low, as wet fur in the cold air may cause the cats to become ill.
Ultrasonic devices emit mechanical waves that are inaudible to humans but are irritating to cats. Though ultrasonic waves are completely harmless, ultrasonic devices may irritate, frighten or disrupt wildlife species. Some ultrasonic devices are equipped with motion-sensing technology, which prevents them from emitting the noises when no cats are present.
Guard dogs are one of the most effective deterrents for cats. Few cats dare to enter a yard that is routinely patrolled by a dog. The dog need not be large, as many small species are especially antagonistic towards cats and are eager to drive them away. Guard dogs should only be used in fenced areas.