We don't have anybody that can guard Dirk one-on-one. Either let him score and try your best to shut everybody else down, or double every time down the floor and leave shooters open.
I know people are going to hate this suggestion, but maybe they need to small-ball it again. IIRC, the only win against the Mavs we got this season was when Duncan was out and we were playing small. Bonner and Dice are zero threat on the offensive end, and we've seen what kind of success they have at guarding him. Put RJ back in at PF and draw up some drives, lobs, etc to make Dirk run on the defensive end. Of course, if RJ plays like he did tonight, there's no point.