The phrase "impregnable in" is correct and can be used in written English.
It is typically used to describe something that is impossible to enter or attack due to its strong defenses or fortifications. Example: The castle was impregnable in its current state, with its high walls and well-guarded gates.
Pakistan are not quite impregnable in the UAE.
"Art is impregnable in what it claims, / Consoles itself while children curl in flames.
Miss Banerjee, who is impregnable in Calcutta but less so elsewhere in the state, has failed to unite the anti-Communist parties.In this section Substance or just style?
That is pretty much what happened to the Yukos oil company, once as seemingly impregnable in Russia as BP is in the West.
People feel impregnable in their cars, more in control, oblivious to the fact that these are machines that deliver injury and death every day.
9 Conor Murray 7/10 He took his try superbly, piercing an English defence that has looked impregnable in the championship.
It is rather like World War I, when stubbornly obsolescent generals wasted millions of lives throwing infantry against impregnable in-depth defenses.
The Kurds' seemingly impregnable faith in America is grounded mainly in desperation — they are largely friendless in the world — and in a kind of pure hope that America will behave in Wilsonian fashion after the war ends.
Doing so would put him in a well-nigh impregnable position in the Republican primary.
The answer for Jacques Lowe, whose images helped create the legend of John F Kennedy, was to store them in JP Morgan's seemingly impregnable vault in Tower 5 of New York's World Trade Center.
I called a couple of times a day — day after day after day — and the calls were not returned, by company people in Omaha who had earlier given me a week of invaluable orientation, including visits to the Union Pacific rail yard in Council Bluffs, Iowa, and to "the bunker," an impregnable building in Omaha where dispatchers control everything that is happening on nineteen thousand miles of track.
