[andyjohnson0]

Directed RF interference oriented at the speakers might work, and could be physically concealed, but will almost certainly be illegal - as well as posing a risk to people with e.g pacemakers and maybe self-driving vehicles. And traceable with an RF spectrum analyser.

Counterphase directed audio? Probably impractical due to range and visible speaker pods.

But obviously the main problem is that you'd be going up against an adversary that is potentially able to use intimidation and violence, and it appears that you don't have recourse to a properly functioning legal system. There are no technological countermeasures against that.