I think someone needs to develop a portable, focusable beam-EMP device. So, you know, those soft, vulnerable electronics inside certain devices can be disabled remotely, invisibly, without such the need for inelegant tools such as angle-grinders and box-cutters.
I'd also say re-used Bluray/DVD lasers to burn out the camera CCD, but that would need to be done very carefully, only angling from above, to avoid risk to aircraft and definitely care to avoid any people nearby.
(I wonder if Flock cameras have some sort of laser-filtering on their lenses?)
Do Flock Camera towers use aluminum in any critical, ground-accessible parts? I hear mercury does nasty things to aluminum. But it's also toxic so would need to be handled carefully.