set (something) in cement
To establish something firmly or permanently; to make something unalterable or not subject to change. The healthcare law looks promising, but we'll have to wait until Congress sets it in cement before we know exactly what it will do.
set in cement
Firmly or permanently established; not subject to change; unalterable. The healthcare law looks promising, but we'll have to wait until it's set in cement before we know exactly what it will do.