password failover

Hello, How do I set up a freeradius server so that if the password fails for the primary radius server it tries the secondary for the password. In my scenario, the primary is up and servicing requests, but the password for the device is incorrect. Now the device looks to the secondary to get authorized and the secondary holds the correct secret for the device. I have looked at fail-over and load-balancing but am not sure if either of these are what I am looking for. Can someone tell me what I am looking for and I can do the rest. Thanks for any help, Jon