Ido this quite often for the reason you described. Put on the motor drive, AF-C and do some short controlled bursts of 3-4 images at a time. Yes, you gotta go through more images at the end of the day, but your potential for getting an in focus shot increases. At least that has been my experience.With proper stage lighting you should be able to stop down further, unless you're going for a shallow depth of field look. If so, there's nothing wrong with snapping a few shots in quick succession and hope at least one of them is in focus.