I think the best thing that we, as a group, can do when the police pull out their "Declaring an Emergency, leave the area" bullshit would be for ALL protestors (esp those in the front line) to TURN THEIR BACKS to the police.
That way, nobody will get sprayed in the face. When the Riot Cops attempt to move the crowd, they will be striking and shooting (less lethal) at everyone's backs. Not only will that make them extremely liable for any injuries and violations of civil rights, it will also make them look like the IDIOTS that they are.
Also, if the cops DO take action and strike our backside, how can ANYONE dispute the fact that we are merely responding to the request to leave, but can't really move due to the large crowd.
Let's all take part in OPERATION BACKSIDE! See ya all at the protest, with my camcorder in hand...