There are several free websites that make it easy to check artiles, duplicate content or plagiarism. Using these sites can help in keeping phrases in your content under control

1. http://google.com

Go to google and copy/paste an entire sentence from one of your articles into google

2. http://articlechecker.com
   
   
3. http://www.webmasterlabor.com/tools/checker/
   
   
4. http://www.copyscape.com/
   
   
5. http://dupecop.com/duplicate-content-checker.php
   
   
6. http://www.articleassembly.com
   
   
7. www.articlechecker.com/
   
   
8. http://www.plagiarismdetect.com/index.php
   
   
9. http://www.dupefreepro.com/
   
   
10. http://searchenginereports.net/articlecheck.aspx