It was supposed to be impenetrable.

It was designed to be impenetrable.

It was designed to be impenetrable, Your Majesty.

It was designed to be impenetrable, your majesty.

He can be so impenetrable.

Therefore, there were no irregularities in the election, and our safeguards proved to be impenetrable:

When they're done, my guess is that hull will be all but impenetrable.