I should start by saying this is super dangerous and you probably should not do this unless you really know what you are doing and why you are doing it. But John Mueller of Google said on Twitter, "The best way to block the traffic from search for specific URLs completely is to disable DNS resolution for the URLs." I think John was being a bit sarcastic in this tweet, because you know, this is dangerous but effective, plus it means users won't be able to access the the page. :) (Yes, he was being sarcastic because you cannot apply disable DNS for a specific URL, it is for the whole site and no one wants to do that).
John added that when you take this approach, disabling DNS resolution, you should see the results in search within a day or so. "It usually takes less than a day to see the results," he wrote.
Here are those tweets:
Google has a lot of documentation on blocking Google, you can read it here.
Forum discussion at Twitter.
