I found in my analytics that at least 3 other domains are mirroring my website by pointing to my ip address. Is there a way to automatically prevent this without having to setup a vhost and 301 redirecting to my website?
Thanks!
Not really. DNS allows you to point any name to any IP address. Often this happens unintentionally as someone points a domain to their droplet and later deletes the droplet or their account but fails to remove the old DNS record.
Apart from creating a redirect or blocking this traffic outright with a firewall on your droplet or directly in your web server configuration you can run a whois on these other domains and try reaching out to the domain owners using the contact email listed (if they aren't using a privacy shield on their domain registration).