Sten make sure you put tape / old tube pieces etc. on the handlebar...that will improve your grip. Always check the map board the day before...really important to tick this off
You have to own a map board to be able to check it prior to competition :P
I've found that strapping tape on the handlebars is the best to stop it moving as it has a rough surface. I have this on the XTC and never have problems. Yesterday on the Anthem I had gaffa tape and it did roll forward although only when I stacked it and landed on the board.
I've got Ori's old map board.
I have tape on the handlebar too; that wasn't the problem. I just hadn't properly tightened the rotating board onto the metal frame, so that started to rattle and come loose, and it made the map rotate around freely in the horizontal plane.