wall of silence

back to the wall

A very difficult situation with no beneficial options available for action.

balls to the wall

With maximum effort or commitment.

bang one's head against a brick wall

To waste effort on a futile project.

blue wall of silence

Strict secretiveness maintained by the members of a police force with respect to information which might be contrary to their interests, especially information concerning questionable police actions.

break the fourth wall

To apparently communicate with reality directly, such as when characters of literature comment on the existence of a reader.

Chinese Wall

An information barrier within an organization, designed to ensure internal confidentiality; frequently used to prevent conflicts of interest.

dead silence

A particularly notable/awkward silence or absence of response.

deafening silence

A noteworthy silence, or absence of response, especially one signifying disapproval or lack of enthusiasm.