Why isn't Clockworkmod Recovery "Sticking"?
I had the same problem and I found the solution is to rename a file in the system folder:


remount /system in read/write mode (use something like the Root Explorer app or ES File Explorer; both have root modes (check the app's settings) for remounting /system as writable)

rename the /system/recovery-from-boot.p to /system/recovery-from-boot.p-bak


(note: you could delete it, but renaming is much safer since its easily reversible)
you could also do this manually in an adb shell or on-phone Terminal session:

mv /system/recovery-from-boot.p /system/recovery-from-boot.p-bak

after you've renamed the file, you might have to re-flash your CWM if it had been missing previously



http://androidforums.com/galaxy-nexus-all-things-root/470831-how-all-things-root-samsung-galaxy-nexus.html#post3712027