So funny. I just built one of these to keep the deer away from the garden. Used an X10 optical sensor that triggers a sprinkler valve...works a little too well I'd have to admit. First, no deer, but the fatal flaw: wind!!!
D'oh, never saw that coming. Espcially since the plants are bigger it takes very little and there are things much smaller than deer that can do just as much damage. And yes, cats hate it.