The robots.txt is still a real thing and works for some search engines, but there are plenty of other ways that our non-prod servers show up in the search results. GoogleBot will respect the robots.txt, but if Google sees links to a non-prod server from other web sources, it will show references to those URL, but not all of the page's meta data. They are consider uncrawled references and it is why those URLs still show up in Google and not because robots.txt is worthless. The nodex meta tag, canonical URLs, and noindex all together, should do the job. I am also installing Google Webmaster tools now for our non-prod servers and should be able to do some work on that side to help.