Sentence examples similar to impregnable equanimity from inspiring English sources

Is that defence impregnable?

The enigma seems impregnable.

"Bell Canada is impregnable".

An impregnable assertion.

So much for equanimity.

"Equanimity" or "tintinnabulation".

His equanimity seems unbreakable.

"Impregnable" was an autoantonym, too.

The double bill looked impregnable.

The horn playing was impregnable.

To many, Google appears impregnable.