For non-public content I think two things go a long way toward that goal:

- nip17 dms

- ephemeral keys

As for public content, I don't know if it's possible to stop people from surveilling public content. I suppose you can theoretically make content that is semi-public by only using relays that require payment to read content as well as to post it, patreon style.

Not sure if such relays exist. If they do, they probably have like two users apiece, so content posted there would not really be semi public. And if any such relay became popular, an attacker could surveil all of its users by paying the fee.