mmmmmm tough one, take them by the throat and tell them not to speak 'til their spoken to. Isn't that simple. thirty five years ago someone took me to one side and said there was nothing wrong with the voice but that I didn't have a "feeling" for the material. It took me years to understand that, years and years, and at the time I didn't appreciate a word of it, "who do you think you are" thought I. Anyway, be resilient and remember all of the criticism even if you don't think it is relevant 'cos one day it might be.