Great question — answering as the UphillTech team:
Thinking out loud.... would something like this work? Recreate your general audience pages by turning them into specific landing pages that interlink between each other (limiting overflow). Then block your subscriber content by programming a token requirement. Subscriber logs in, user ID verified, password matches, token authenticated. Subscriber moves about the subscriber portal using the random token it was assigned. Web crawlers cannot imitate the token process, so they gain no access to the subscriber portal. Tokens expire after xx minutes of inactivity.
Full answer by elbrant: https://webmasters.stackexchange.com/a/141518 (CC BY-SA 4.0).
Need it done for your business? UphillTech.