Resegnation is a fact of life that cannot be prevented by any rules. The best rules can do is put a sanction on doing it, and the worst imaginable sanction is an individual game is that you would lose. Which is exactly the idea, and thus has zero value as a deterrent. You will have to find a better solution for when one of the palyers forfeits (e.g. loses on time because he simply walked away).
I have edited the resignation rule to remove the constraint on resignation.
I have edited the resignation rule to remove the constraint on resignation.