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If a page URL has Google Analytics query strings, does the page need a canonical tag? e.g., something.com/?utm_source=newsletter&utm_campaign=mar-2013-nsl I have rel=canonical on all our pages because some of them will be accessed via URLs that have non-Google strings. The strings are only for marketing purposes, not for identifying a specific page to display. e.g., something.com/?source=acme Should I only implement the canonical tag on the pages that might have non-Google marketing strings in the URL?

I'm implementing landing pages that are optimized for specific keywords. Some of them are substantially the same as another page (perhaps 10-15 words different). Are the landing pages likely to be identified by search engines as duplicate content? How different do two pages need to be to avoid the duplicate penalty?