( of a building ) to be strongly built, often with many locks, strong doors, guards, etc., so that it is difficult for people to enter and the things kept there are safe :
This home of yours is like Fort Knox.
( of a building ) to be strongly built, often with many locks, strong doors, guards, etc., so that it is difficult for people to enter and the things kept there are safe :
This home of yours is like Fort Knox.
Oxford Advanced Learner's English Dictionary. Оксфордский английский словарь для изучающик язык на продвинутом уровне. 2005