Unless you want to resort to an Orwell like surveillance level in every frum community, this would be impossible to ascertain.
What would you do? Hire private investigators to dig through peoples lives and put all of your evidence before some newly established beis din? Or just put a gun to every Rav and mechanechs head and have them declare their loyalty to Hashem?
By the way, Orthoprax people are “off the derech” in private, they don’t recruit and in no way rock the boat. So before you start a witch hunt, realize that there are bigger fish to fry in the frum world.