unshakable
     adj 1: marked by firm determination or resolution; not shakable;
            "firm convictions"; "a firm mouth"; "steadfast
            resolve"; "a man of unbendable perseverence";
            "unwavering loyalty" [syn: {firm}, {steadfast}, {steady},
             {unbendable}, {unfaltering}, {unwavering}]
     2: without flaws or loopholes; "an ironclad contract"; "a
        watertight alibi"; "a bulletproof argument" [syn: {ironclad},
         {unassailable}, {watertight}, {bulletproof}]
Source: WordNet® 2.0