I’m familiar with that story and I’m aware that balloons contribute to the problems of plastic ingested by wildlife and an abundance of micro plastics in the environment. And I also understand that helium is getting scarce.
To be clear, I’m not suggesting anything like a mass balloon release.
What I am suggesting is distributing a helium balloon to a percentage (off the top of my head, say 5%) of protesters, held by a thin thread perhaps 5-7 metres long. The idea being that the balloons would swing around randomly in the breeze and the threads would create a flight hazard to any drones below that altitude.
I’ve no idea if it will work or not, but it’s simple and it’s cheap and it seems plausible.
And as generic_name pointed out, it has built in plausible deniability.
Helium is scarce and expensive. Hydrogen’s not scarce though: aluminum or zinc pieces in a soda bottle half full of dilute hydrochloric or sulfuric acid will fill balloons. If there are connecting lines between the balloons as well as the people holding them, you can cover more area with fewer balloons, as well as covering area that looks safe to fly through.
Yes, yes and yes. I’d be very cautious also about any supercapacitors and flat shaped cells hidden inside. Capturing the drone using a (metallic?) net launcher, then putting it into a metal box and dismantling it in a underground place might be effective and safe. I would however get rid of the recognizable parts ASAP then document anonymously any reverse engineering or just details about the construction, weak points etc.