It was found by locals who kept its existence secret at first.

The most senior wanted her to keep its existence secret.

It's important that we keep the drug's existence secret,' said Max, 'especially from our clients.

They'd be able to keep their existence secret.

They survive by borrowing all they need from big people and try to keep their existence secret.

They are very, very few and try to keep their existence secret.

As for keeping our existence secret, it is utterly necessary if we are to survive and increase.

They kept its existence secret because neither wanted to stir up gossip about their relationship.

If such prisons exist, it has always been the intention to keep their existence secret for ever.

In Bloodlines, vampires are sworn to keep their existence secret.