If you need to hide pages from search results, use the right tool for the job....

https://www.tumblr.com/distantlyperpetualharbinger/811808907244797952/should-i-block-a-page-behind-a-login-to-remove-it

If you need to hide pages from search results, use the right tool for the job. Add a "noindex" meta tag to tell Google to drop the page from its index during the next crawl