As one of the leading contested marks of the comp over the last 10 years, Richo you really don't need to duck your head when you feel a small push in the back. You're far better than that. 7 out of 10 times you will beat your opponent one on one, no need for the theatrics. Umpires are aware of forwards who try to milk free's. Keep your stance and just try to mark it, regardless of the pressure from behind, free's will take care of themselves 