Some methods for keeping cats off cars include electronic devices for repelling animals and corrective behavior when the car owner sees the cat on the car. Electronic devices use water or ultrasonic sound to scare the cat away. Corrective behavior can include spraying the cat with water or making noise.
Another method for keeping cats off cars is to cover the car with a tarp or car cover. Methods not recommended for keeping cats off cars include surrounding the vehicle with cayenne pepper, mothballs, lemon or other household items said to repel cats. These substances generally don't work on all cats, and some may harm the animal.