How to completely close out of apps in iOS 6?

I own an iPhone 4G and I recently upgraded to iOS 6 and I wanted to ask, how do I completely close out of an app on iOS 6? Because I've tried double tapping twice and then clicking the x on the apps, but it still seems to come up in notifications (for example when i get a new Kik/Facebook Message) and that takes data, is there any way to completely close out of the apps? (As I said I've tried pressing the home button twice and making the apps wobble and then clicking the x, still doesn't work, still comes up in notification centre)

Go in settings and turn off the notification for that app or all