Unchallengeable

A century ago, a very distinguished Swiss military writer, who saw much service throughout the Napoleonic period, who studied minutely many of the principal campaigns, and who reflected profoundly upon international relations as affecting war, and as affected by it, stated as a fundamental necessity of the European Balance of Power that no one State should be permitted to acquire an unchallengeable naval superiority.

Source: wiktionary

With a solemn imprecation on the formality and absurdity of the writer, Lord Etherington let the letter of advice drop from his hand into the fire, and throwing himself into a chair, passed his hand across his eyes, as if their very power of sight bad been blighted by what he had read. His title, and his paternal fortune, which he thought but an instant before might be rendered unchallengeable by a single movement of his hand, seemed now on the verge of being lost for ever.

Source: wiktionary

The Policies of Parties admitted to the "Second Class of Select Assurances" shall be subject to the existing Conditions of the Company as to residing or travelling beyond the limits of Europe, and as to Military or Naval Service; but with these exceptions, and subject to payment of the ordinary Premiums, shall also be absolutely unchallengeable.

Source: wiktionary

Like most prisoners, Eddie Jones is serving an indeterminate sentence, meaning the time he actually spends behind bars depends on the decision of a parole board, a decision not subject to the due process requirements of the Constitution. And where he will spend that time, whether in a harsh maximum-security prison like Walpole or in the relative comfort of an institution like the Southeastern Correctional Center, depends on the equally unchallengable decisions of prison authorities.

Source: wiktionary