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I love reading these in-depth answers from the CEO of Moz. It's so nice to see a hands-on CEO taking time to deal with even more mundane things like discussions around support issues.

I used to use a comments program on my website that created comment pages in the form of http://www.example.com/web-page.htm?comm_page=2. When I switched to a new comments program, I worried that these old comment URLs would be considered duplicate content. I created a 301 redirect that, for example, would redirect http://www.example.com/web-page.htm?comm_page=2 to http://www.example.com/web-page.htm and disallowed them in robots.txt, which I later learned was not the thing to do.. I have removed the URLs from being disallowed in robots.txt. However, many months later, these comment page URLs keep appearing in Google's index from time to time. I use the "Remove URLs" tool in Google Webmaster Tools to remove the URLs from Google's index, but more URLs appear a few days later. How can I get rid of these URLs for good?

Thanks!