While those of you in charge might have thought of this already, may I suggest limiting account creations to 1, based on IP addresses? Or, could you investigate suspicious duplicate "troll" accounts based on user reports? That is, if this is an issue. If limiting accounts is an option in the configuration of this forum, that will work for users with static IP addresses. If their IP is dynamic, and a random new account is reported as suspiscious, you can check the ISP/location of the user through websites such as IP Tracker, or others. A match between a reported user and one known for causing problem would unlikely be a coincidence.