I found out via the Scott Bourne (Photofocus) twitter feed that Canon is offering a locking mode dial modification for the Canon 5D Mark II and Canon 7D bodies. Unfortunately, the modification does require the camera body to be sent in to the Canon Service Center and will cost $100 for US customers.
Accidental movement of the dial has always been one of the few complaints I’ve had with my Canon dSLR bodies, especially since I often use a Black Rapid camera strap which puts the camera to my side, which occasionally results in accidental Mode Dial movement. It’s irritating to bring your camera to the firing position and take a shot only to realize you some how got moved from M or Av to P or Bulb mode.
I’m probably going to get my bodies modified for this, but I’m waiting a response from Canon regarding any price difference for Canon Professional Services members and the expected turn-around time for the work.