Well, no. The paladin's DC trick is just as effective as the fighter's interrupt attack, if not more so. DC does damage once per round, fighters only get one immediate action per round, so in the end they can both do their thing once per round.Yes, I realize it's not as good since it applies only to the first attack the marked creature makes before the Paladin's next turn, but I think I'm going to start using it with my Artful Dodger Rogue with Defensive Mobility, since the DM refuses to make a move that will trigger the DC damage.