is it a good practice to delete the AdBannerView on viewWillDisappear and add it back on viewWillAppear?

I am currently doing the following in my code avoid the issue of "obscured" ad. But is it a good practice? One potential problem is that - assume before the viewWillDisappear, there was an ad request send out, and then when the ad come back the adBannerView instance has gone. Would that be a big problem? Should I only do hideAdBanner instead?

- (void)viewWillAppear:(BOOL)animated {

    [super viewWillAppear: animated]; 



    // create the ad banner view

    [self createAdBannerView];



    if (adBannerView != nil) {

       UIInterfaceOrientation orientation = self.interfaceOrientation;

       [self changeBannerOrientation:orientation];

    }

} 



- (void)viewWillDisappear:(BOOL)animated { 

    [super viewWillDisappear:animated]; 



    // iAd

    if (adBannerView != nil) {

        [self hideAdBanner];

        adBannerView.delegate = nil;

        [adBannerView release];

        adBannerView = nil;

    }

}