I'll often begin browsing on internet or even have taken bathroom breaks while my melee is tanking one of them rat bosses, those rat bosses hit like a mongbats (it feels like so with max DCI, Resist, Parry/Bushido, and HCI+life leech) but they have a trillion fazillion hit points so I notice people get tired of putting in the time to kill them, even if they are capable.
So another option is to increase the damage those rat bosses do by a whole lot and also maybe have them cast paralyze/teleport/dismount spell too, so that way they have better chance of killing them griefers, teach them a lesson, and scare them off from trying to lure again, while making those rat bosses interesting/fun to fight.