Local home improvement stores have an awesome tool to deter graffiti vandals, Wireless Motion Activated Alert Sets. The wireless motion activated alert set comes with a motion sensor that can detect movement over 65 feet. When the motion sensor is tripped, the audible box that's plugged into an interior electric outlet will beep. The audible box also has a lamp plug-in that will allow a lamp to be turned on if the motion sensor is tripped. If used correctly, these will help you deter most graffiti vandals.
My Graffiti Removal Guy recommends using some of these ideas when setting up a wireless motion activated alert set. Motion sensor should be placed in areas highly targeted by graffiti. If the property hasn't had a graffiti problem, the sensor should be place in areas where you feel the property needs an extra set of eyes. Once you found a suitable place for the sensor, its recommended to paint or camouflage tape the sensor housing to keep it better concealed. Choose a window closest to the motion sensor to place a lamp and plug in your audible box. Once you audible box is plugged in, plug in the lamp and go outside to test it. The light should come on as someone approaches the area. You may need to adjust the sensitivity of the sensor if you want it more, or less responsive.