- (void)didMoveToParentViewController:(UIViewController *)parent
{
	[super didMoveToParentViewController:parent];

	if (![parent isEqual:self.parentViewController]) {
		NSLog(@"Back");
	}
}

Inserted into a view controller pushed into a UINavigationController stack, this will fire the ‘back’ message when the user presses ‘Back’ to back up the view controller stack.

As seen on Stack Overflow…