A FERVENT CROWD of 100 or so activists gathered in a circle, chanting in the dry oasis beneath the Burnside Bridge late Monday, October 3. Bike commuters and joggers craned their heads to check them out. The homeless campers who usually inhabit the spot were amused.

Once, twice, and then a third time, the crowd shouted in unison: "Officer, I'm going to remain silent. I want to see a lawyer." The man in the middle of the circle, flannel-clad defense attorney Kenneth Kreuscher, wasn't satisfied. After a brief pause, he made them say it one more time. And then he went on to another topic—still hammering his main point: "It is dangerous to talk to the police."

Kreuscher, working with the National Lawyers Guild, was delivering a brief, energetic lecture called "Know Your Rights"—essentially all about how not to get arrested during a rally and what to do in case you are. He was invited by the organizers of Occupy Portland, the anti-corporate group planning a noontime rally Thursday at Tom McCall Waterfront Park, followed by a march to Pioneer Courthouse Square. (And then, likely, followed by days of camping out along the Willamette.)

Hundreds of activists are expected to show—setting up an inevitable clash, even if it's a quiet one, with Portland cops. Will you be at the rally? We took notes during Kreuscher's lecture. Here's what you need to know.

Cops Are Tricky

Not only have cops been known to go undercover to infiltrate rallies, but they can also lie and commit some crimes as part of their missions. Sometimes, they may even pretend to be your friend, encouraging you to commit a crime. Entrapment, Kreuscher says, is a difficult and very specific legal principle to prove—so don't expect to rely on it if you suddenly find out your "friend" is actually the fuzz.

Don't Talk; Walk Away

Kreuscher says some officers will try to make small talk with protesters, something that can get them to unwittingly incriminate themselves or others. Unless a cop is compelling it, you can treat a cop like anyone else: "You don't have to speak to an officer on the street unless you choose to." The best thing, Kreuscher says, is to be unfailingly polite but say you're busy and then walk away. That's key. If you stay put, you might eventually relent and start chatting.

Ask for a Lawyer

Kreuscher was drilling the crowd on this point. If an officer detains you or steps up an encounter, loudly say you'll be silent and ask for a lawyer. Most cops, he says, are trained to shut up when an attorney is invoked. And judges, he notes, also frown on cops who don't respect that.

Don't Lie to a Cop

Sometimes they're FBI agents, not local cops, who are shadowing you. If you lie to a federal agent, even possibly by giving a fake name, you could wind up charged with a federal felony and face five years in prison.

Never Allow a Search

If you ever feel like a cop is trying to peek into your bag, subtly or not, loudly say, so there are witnesses: "I DO NOT CONSENT TO THIS SEARCH." This is especially important if someone else might have held your bag for you at some point. You might not know whether they put something illicit inside it. Kreuscher says when he reads a police report where a defendant said this, "It makes me love them. They didn't screw themselves."

But even if you heed Kreuscher's advice? You still might get arrested. Or worse. "It's not a magic wand," he says. "It's just a way of making a shitty situation less shitty."