Dealing with infiltrators and trolls

http://www.schnews.org.uk/archive/news755.php

This article claims that British police surreptitiously posted to indymedia.org sites, trying to incite violent action or at least sow discouragement.  These very posts made by the police, then, could be used to prove the dangerousness of the proposed action:

"It should be remembered corporations seeking injunctions under the Protection from Harassment Act (link) have relied heavily on comments made on Indymedia as evidence. This act has been used against campaigns such as Smash EDO to criminalise all forms of dissent targeting specific companies, even entirely peaceful and completely legal protest."

This is a problem for ICA.  Since the structure of the collective action is essentially leaderless, how does the organizing prevent infiltrators and trolls, who want to either derail the project or at least discourage it's participants?  Basically, the rest of the participants have to call out and refute anyone who tries to take the project off target or promoting illegal or non-approved methods.  During the beginnings of Project Chanology probably many people where were not infiltrators were nevertheless accused of being OSA (Scientology's Office of Special Affairs, their dirty tricks department).  No doubt some people who shouldn't have been were driven away, but the result was that the project stayed on target without illegal actions being done.  So once again it is everybody's role to prevent infiltrators, trolls, or anyone else from derailing the project at hand.