Block/remove one WP-Multisite Subsite from search engines

Hi
I have one subsite of a wordpress multisite network, which must not be found on search engines. This subsite should be kind of private, but without a password.
I checked in the wordpress settings that this site should not be found on search engines - but I wonder if that is enough...
or is there a better way to make it more "private" without a password?
Thanks