Impenetrable in a sentence?

His skin was impenetrable, Impenetrable means difficult to get through such as a forest or your skin. the forest was impenetrable and it took me hours to get through.

The man had impenetrable metal skin, incapable of being pierced.

Impenetrable- The fort's defenses were thought to be impenetrable.

When it has a subject, verb, punctuation, capitalization, a predicate, and a complete thought. A sentence is a sentence when it is handed down by a judge (or a magistrate).

The professor's heavy accent made the substance of his lecture nearly impenetrable.