inexpugnable

adj

1. Impossible to eliminate or destroy; impregnable.

   “My one hope of the world, my inexpugnable consolation in looking at the miseries of the world, is that this is altering.”

   “It crept into one's mind, a distress as vague and inexpugnable as a sea fog on a spring morning, and presently one shivered and wanted to go indoors...”

   “This seemed to be an inexpugnable refuge, where we could live untroubled and learn to know each other."”