Re: Keystone Cops
You try filming "the sky" for "an hour or two". Then watch it to see if there's something that might possibly be a drone flickering somewhere in the distance.
Bear in mind "the sky" is more than just one direction, so it's going to take a lot of cameras to watch the whole thing.
Let's make up some numbers, just for fun. Let's assume (optimistically, but you gotta start somewhere) that the drone is going to be 30 cm across, in whatever dimension we happen to see it. And we want to be able to spot it at least 2 km away. At that range, it's going to cover an arc of about 0.008 degrees in the sky. If your camera records a picture width of (let's say) 4000 pixels, then a single camera can be trusted to watch about 30 degrees (horizontally, about half that vertically) of sky at high enough resolution to capture the drone as a single pixel. (That's assuming the camera doesn't use some kind of lossy compression, of course.)
So, set up 30 cameras to watch 180 degrees of sky to a height of 75 degrees. In the rain. When you've analysed the resulting 30 hours of video, let us know if there was a drone in it. I look forward to hearing back from you. (And note that the area this experiment monitors is only a small fraction of the exclusion zone described in these rules, so a negative result is still far from conclusive. To cover the whole area, you'd need to be watching - considerably more cameras at this resolution.)