I have two solutions for you, giving that you cannot add a target or action to your back button:
1- Add a new barButtonItem and call it whatever and add your selector to it, and put it in the navigationItem.leftBarButtonItem. Don't forget to pop!
2- Override the viewWillDisAppear method, and do whatever you wanna do there.. if your viewcontroller doesn't direct you to another viewcontroller but the previous one...
if you have any more questions, just ask (Y)