I was thinking about this overnight I think your group should have multi layer approach because each thing on its own can be defeated. 1 perform background checks on new members without their knowledge 2 have a code of conduct that if broken by anyone means they are out of the group. For example if a topic is off limits until a certain rank is met then you found them 3 use the lobby structure to advance "rank". I saw that's how some secret societies including the masons handle promoting inside without making the advancement strategy known 4 make red-pilling part of the organization so that if a fed does get in they might grow a conscious from the constant exposure to the truth. 5 disinformation tests where you tell one person something wrong intentionally and see where the info ends up 6 have a website with a forum and check logs for ips then cross reference those. Or some other digital method to keep tabs on group activity. Like conduct all business via some digital method where you can check its 7 keep the group relatively small and local but perhaps have a chapter system The infiltrators are like spies and I think there are lots of books out there about how spies were discovered or turned during cold War times.