Her arguments seemed 'impregnable'.
an 'impregnable' reputation
an 'impregnable' fortress
(..) Five minutes in his flat. Four floors up. That's why they think they're safe. Put a chain across the door, bolt it shut, think they're impregnable. They don't reckon for one second that there's another way in. I don't understand. Dealing with a killer who can climb. What are you doing? (..)2010 TvShow: Sherlock Title: The Blind Banker Season: 1 Episode 2