Director instruction which ruins a lot of shots, how to prevent it?

"Non-singing guitarists, bassists and drummers keep their lips closed without mouthing lyrics, except for a non-singing expression explicitly requested by the user; their hands and bodies continue the instrumental performance"

This often invites musical players into scenes where you don´t want them, I have no idea how to get rid of it, I have tried with negatives and positives, nothing seems to work.