How do you handle the dreaded ........

How do you or should i say what would you say once the dreaded topic of your termination from a job comes up. How would you phrase it and how do you handle it? I really don't want the potential employer calling up former employer and she ripping me to shreds with negativeness and potentially loosing job because of her comments that would be made.

Isn't there a law that if a ref check is called they can only give dates of employment only and no reason as to why person is no longer employed? and can you request to not contact former employer at local level and contact at a corp level( completely in another state) where they dont know the at hand reasons/issues which lead to the volitile fall out?