There are a lot of guides and videos on this topic. Just search on Goggle for "WLC anchor" and you will find what your looking for. Here is a few:
http://www.cisco.com/c/en/us/td/docs/wireless/controller/7-0/configuration/guide/c70/c70mobil.html
http://mrncciew.com/2013/03/22/auto-anchor-mobility/
-Scott
*** Please rate helpful posts ***
-Scott
*** Please rate helpful posts ***