There should be a specific time before the end of dueling phase that decks must be posted by (for challengers). As it stands now an illegal deck can only be discovered after the fact - it can very often turn a 3-1 into a 2-2 that needs a replay (either disrupting the event by making everyone wait or inappropriately awarding a win). If for some reason we won't require them after the match, at least set a time (say 3 days before phase end?) or make people PM.