I understand how to do basic keyword research and how to review a competitor's code (meta tags, etc.).

But what is the best method for finding out what a competitor's target keyword is for a particular web page?

For example, the URL www.example.com/about-us, what is the best method for finding out what their target keyword is? I have been using a keyword density tool to run the URLs and find the keyword or phase that appears most often but would think there is a better way?