Creating domain-level privacy is supported for PRO accounts. If you are a PRO:

As a PRO customer, you can choose what specific website you want to allow your deck to be embedded on.  With domain-level privacy, you no longer have to worry about your decks getting into the wrong hands.

To add domain-level privacy

  1. Click Edit Deck on the presentation needing additional privacy
  2. Scroll down to Embed Visibility 
  3. Choose from Everywhere, Nowhere, or Specific Domains
  4. If you choose Specific Domains, enter the URL of the domains that you want to restrict embedding to
  5. Click Save this deck to save your changes
  6. Embedding will now only be allowed on the domains you added