Most legit search engines are going to honor robots.txt and you can disallow access.
Next level would be using something like rate limiting controls and/or Cloudflare's bot fight mode to start blocking the bad bots. You start to annoy some people here.
Next would be putting the content behind some form of auth.
https://developers.cloudflare.com/browser-run/quick-actions/...
Even when we do actually put physical locks on things they are mostly there to show that someone breaking in did so intentionally and not at all designed to prevent motivated attackers.
Where do you live? In the US it’s actually illegal for anyone except the USPS to deliver to a mailbox.
Also this has gotten pretty far away from the web scraping scenario. There’s no door accidentally opening here.
That being said you would require your user to download a compatible browser for gemini/gopher.