The FBI is mounting a quiet but concerted effort in congress to revive their domestic intelligence operations. Under current congressional over sight mandates on domestic intelligence the FBI is limited to investigating only suspected criminal acts by individuals who belong to "subversive organizations" but they are not permitted to investigate the organization itself. Since early 1992 the FBI has been cultivating informers within the patriotic movement in anticipation of having congressional oversight restrictions reversed.
One method to reduce the risk of compromise is to require each member of your militia or organization to swear or affirm an oath worded as follows: "I (state name) have never been, am not now, do not contemplate nor intend to be in the future, a local, state, federal or international law enforcement official, nor have I ever been, am not now, nor contemplate or intend to be in the future, an informant for any local, state, federal, or international law enforcement agency."
This must be done individually.
A simpler method is to ask: "Are you a cop?" Then: "Are you an informant?" These are yes or no questions and require a "yes" or "no" response.
We know it is ugly, but it is a necessary security procedure. If they say "no" any evidence they collect is considered entrapment.
For now, at least.