Local home improvement stores have an excellent 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 has 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 activate if the motion sensor has 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 sensors should face areas highly targeted by graffiti. If the property hasn't had a graffiti problem, the sensor should face areas where you feel the property needs an extra set of eyes. Once you found a suitable place for the sensor, you can 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 your audible box has power, 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.