put (or raise or stick) your head above the parapet speak out about something in spite of the risks involved.

☞ A parapet is a protective wall along the top of a trench or similar military emplacement. Anyone showing their head over the top of it would be liable to be shot.

2013Daily Telegraph The irony is that there is latent talent in Whitehall, although it is very difficult for good civil servants to stick their head above the parapet.