ip route x.x.x.x x.x.x.x y.y.y.y
ip route x.x.x.x x.x.x.x z.z.z.z 200
The x.x.x.x is your source address and mask and y.y.y.y and z.z.z.z will be your destination routers. if you are defaulting everything to the internet the set of x's need to be 0's the 200 at the end of the 2nd route is the administrative distance. Now, if the y router fails and can't be reached the z will take over. You need to replace the X Y and Z values with your IP addresses in your environment
