http://www.intergas.co.uk/CH3SH_addgas.html

Some Mercaptan CH3CH2SH could be the smelliest substance around, I hate to think what a full release of it would smell like, seeing as it's parts per billion when added to Natural Gas.

Although it is toxic and would smell like a gas leak so one of the other volatile thiols would be better.

I don't support destructive protests, but this "scent bank" idea plus all the dog training must be costing quite a bit. And it seems the plan might so easily be disrupted...

What happens if everyone who thinks [dawn raids, very subtle] they might have, umm... been sniffed, trades 3 weeks of their dirty clothes with a number of grandmotherly protesters? Or collects 50 pairs of unwashed socks and distributes them for people to tie around their belts?

I wonder how much a radical shift in diet for a week, plus shaving all your hair (old scent in that, presumably) plus living in a different location for that week would change one's scent?

All the protesters dust their pants with cayenne pepper? Would a snort of that put a dog's nose out of commission for a few hours/days?

And so forth.