I never did.
I don't go for the game any more, but as a teen, we would purposefully devise experiments to keep anyone from being able to move the planchette.
We would often have one person *think* the question, and then nod when the question had been asked. Then, two others (usually me, but never the questioner) would be on the board for that person to answer the silent question. Then, board users have no way to "know" if it's a yes or no answer, or spell something out.... etc etc. It worked well, for us.
To keep others from doing this, we also practiced minimal touching (one fingertip, not the whole hand's fingertips) and sometimes the board users would also experiment with placing a hand on the planchett, but looking away from the board, so they couldn't see what the planchette spelled.
Interesting poll....