There really isn't much that can be done about trolls who are tech savvy and know how to manipulate people and information to their advantage. IP banning does nothing to control such things these days and in trying to get rid of them you will be left with their fanclub who calls you names and acts out because you banned the "wonderful member just trying to voice their opinion." Trying to deal with things while they are in their infancy and deleting/editing/etc topics and conversations that go this way are your best bet. Show them they can debate but not flame/fight and they may go elsewhere.