Best way to "unqualify" an candidate?

Best way to "unqualify" an candidate?

When there's a candidate we want to "unqualify" as a candidate, what's the best way to do that? I recall there was an "unqualify" as a candidate option in the past.

We have a candidate who we will not work with in the future. We don't want to remove him from the database because we don't want a future recruiter to add him to our database. We've done email opt-out, but want to make sure he doesn't show up in any search results.