ironclad

ironclad (http://definr.com/ironclad)

     adj 1: inflexibly entrenched and unchangeable; "brassbound
            traditions"; "brassbound party loyalists"; "an
            ironclad rule" [syn: brassbound]
     2: without flaws or loopholes; "an ironclad contract"; "a
        watertight alibi" [syn: unassailable, unshakable, watertight]