This sounds like a case where the problem of collective action would actually work in society's favor: a single vandal would bear the full cost of destroying the sensor (e.g., the risk of getting caught), but the "benefits" of the destroyed sensor would be diffuse, spread out to all would-be shooters.
At this point you have to compensate the individual enough by, e.g. paying much and/or providing proper equipment[1].
[1] - I imagine a proliferation of cheap microwaves converted into portable battery-powered anti-electronics weapons. And how do you protect UAVs against that?
http://en.wikipedia.org/wiki/Collective_action