I took a used cat litter bucket, a Passive Infrared Sensor (PIR), an ARDUINO micro processor, an LED clearance light, a wind shield washer pump and a 5 volt relay to construct my device. When ever the cat approaches the area I am defending the PIR sensor picks up the cat's body heat. The program in the ARDUINO activates the LED light and the pump. Noise, the yellow light and a fine spray of water deter the cat from going any further.
It works just as well on the cats as it does on my big feet.