By search engines, di you mean things like Google?
If so a simple solution as these small updates I suspect are just related to your community
Create new category
- Category Security.
- Delete Everyone See/Create/Reply
- Add Trust_level_0 See
Add your staff/mid or group that is allowed to create and reply to topics. With the Tl0 you can of course add other permissions needed ie reply.
This will make topics in this category only viewable by logged in users Vs Everyone that allows non logged in users to view topics and this allowed crawlers to index public viewable content