Hi - okay that's a good answer to the question I asked but I should have given a different example of dynamic navigation.
Go to a foo.com and the navigation reads a drop down say "available cities" with six cities including new york. Now go to foo.com/newyork and the available cities no longer has newyork but instead the five other cities the site supports. In effect, you need the navigation to not include newyork as it is now in the URL.
Another example - login to a site and you see a navigation that's specific to certain characteristics of the experience of the user. Go to New York and the navigation shows navigational elements specific to services in new york. Different when you go to Chicago.
Somehow/someway you need to trigger the navigation to be different based on some conditional logic. Thoughts?