Is there a suitable material for a lightweight "roof" you could put over your property that would block aerial photography but still allow sunlight and rain to penetrate?
One could even make it shielded against electromagnetic frequencies. No more drones hacking your wifi!
Is there a suitable material for a lightweight "roof" you could put over your property
Yes, well-placed trees, plants, and some lattice material.
I once visited the roof of the Limn building on Townsend in San Francisco. It turns out there was a lush garden, nice eating areas, and an Airstream trailer, all on the roof. Absolutely none of it was visible from the ground, and you'd be lucky to make out much of anything from overhead.
Camouflage netting is perhaps the only surefire way to do this, although I'm sure that will attract far more attention than doing nothing at all. Something that would work kind of OK would be to create a large radiometric difference in your property like having a dark black roof and making your lawn as reflective as possible (white cement or gravel, swimming pool). That way when the imagery is processed in an automated fashion it will render your area badly. It still would be possible to go back to the original images and enhance the area manually but can be quite a chore.
Build your property (partially) underground? Like this http://www.trendir.com/house-design/grass-roofed-home-built-... or similar. You'd need to deal with waste heat somehow for the infrared signature not to look suspicious. And ground-penetrating RADAR would pick you up as well, I expect.
One could even make it shielded against electromagnetic frequencies. No more drones hacking your wifi!