Mana points refreshing...

[Yogi_Baar]

Use such rules that players aren't allowed to carry any potions, books or money when entering a duel game. Get an impartial judge (or a partial one for each dueler) to scan both parties and make sure they don't talk to any vendors in the game. All 3 (or 4) should enter the desired dungeon level, with the judge(s) clearing the level (or room, or whatever) and picking up any dropped potions. Then the judges cast a guardian and retreat from the level (or leave the game, if that doesn't remove the guardian).

Should work.

But for crying out loud, switch to IronMan tournaments. Dueling is... well, whatever floats your boat, I guess.