I belong to a relatively closed group and the only way a woman can get into the group is if she is brought in by one of the women in the group. We all prefer discretion, so typically a woman will be introduced to one of the bulls by a female member. To get the introduction there has to be a consensus among the women. If things go well and she wants to continue she is slowly assimilated into the group. If she can't be discrete she never gets past the one bull that fucked her first. Same basic rules apply for new bulls except they must be approved by the bulls in the group.