The potboy at the corner, who is a privileged amateur, as possessing official knowledge of life and having to deal with drunken men occasionally, exchanges confidential communications with the policeman and has the appearance of an impregnable youth, unassailable by truncheons and unconfinable in station-houses.
There are no more uses of "unassailable" in the book.
Show samples from other sources
But worst of all for Helene, the vultures build their nests above the clouds, atop the most unassailable peaks.
Sabaa Tahir -- An Ember in the Ashes
Everyone had pitched in to help out, even the people she usually thought of as almost unassailable in their reserve: Kadir, Jia, Maryse.