Why do you want that? I like the dueling system
Without serious anti-grief stuff (ie you can't attack anybody at all ever) people will get griefed. I will tell you right now that when a duel is taking place and both guilds are spectating, when you redline your opponent his guild will MA you and both of you will get restored to full HP.
I'm assuming you don't like how trammies crowd the no-pvp spectator zones around the pits? Well... take out the safety for spectators. Have duels start anywhere on the map, take place in the duel pit where people risk life and limb to come watch, and then after the duel the duelists are teleported back to the starting location without any risk at all of the duel being interrupted.