We are still in this together, but "this" is going to be real different in the very near future. This demands a different kind of "we."
The French Resistance during Nazi occupation played important roles delivering downed Allied airmen back to safety, supplying military intelligence, and acts of sabotage.
The Underground Railroad is estimated to have brought 100,000 freedom seekers to safety between 1810 and 1850.
It's time.
TL;DW:
That last one sound the least plausible, but most karmically appropriate tactic.
But basically tldw is: Earplugs or better passive hearing protection.
Sound has to cross all of the mediums they propagate through. At every change in medium, some sound will reflect. The reflection is greater the bigger the difference in mass and/or stiffness.
For regular, spherical spread sound a lot of it spreads widely and laps around edges (like waves around a pier, a bit flanks around). For narrowed/concentrated waveforms, this is lessened.
Thus a barrier stiffer and/or heavier than air does make a difference, about 3 dB per doubling of mass and/or stiffness, a riot shield will probably give you about 10 dB.
The effect is higher if you do a double barrier with air in between. A two-pane window can easily do 20 dB. Probably the same with a two-pane riot shield.
This article suggests hearing protection (ear plugs) against hearing damage, and dodging perpendiculary from police or vehicle to escape the beam.
On the topic of speculative countermeasures, possibly a water based system could help. NASA uses a Deluge system, essentially spraying water at the noise to scatter and absorb it.
Would probably require quite a lot of water, maybe a hose, tank, hydrant or similar.