I am getting married soon and my future wife's credit is bad while mine is very good. How can I protect mine.

It will be very difficult to avoid having your marriage affect your credit score. However, you can mitigate the affect it would have by not having joint bank accounts/credit cards and not taking out a mortgage together. Conversely, if you choose to do any of these (and manage them responsibly), you may be able to help your wife's credit rating over the long term and while you may take a ding or two right away, you should be able to build your rating back up over a year or two.