keep adbanner at bottom on all orientation in iOS?

Question

Iam trying to place one adbanner(admob banner) on bottom of my app.But currently by using my code it appearing sometimes at bottom or middle like that.Please check following screenshots

please check my code

#import "LocViewController.h"
@interface LocViewController ()
{
    UIInterfaceOrientation orientation1;

}
@end
 #define MY_BANNER_UNIT_ID @"a152a98e7f64210"

@implementation LocViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    // Create a view of the standard size at the top of the screen.
    // Available AdSize constants are explained in GADAdSize.h.
    if([UIApplication sharedApplication].statusBarOrientation == UIInterfaceOrientationLandscapeLeft||[UIApplication sharedApplication].statusBarOrientation == UIInterfaceOrientationLandscapeRight)
    {
        //Do what you want in Landscape Left
        bannerView_ = [[GADBannerView alloc] initWithAdSize:kGADAdSizeSmartBannerLandscape];
        bannerView_.frame = CGRectMake(0,678,bannerView_.frame.size.width,bannerView_.frame.size.height);
    }
    else if([UIApplication sharedApplication].statusBarOrientation == UIInterfaceOrientationPortrait||[UIApplication sharedApplication].statusBarOrientation == UIInterfaceOrientationPortraitUpsideDown)
    {
        //Do what you want in Portrait
        bannerView_ = [[GADBannerView alloc] initWithAdSize:kGADAdSizeSmartBannerPortrait];
        bannerView_.frame = CGRectMake(0,934,bannerView_.frame.size.width,bannerView_.frame.size.height);
    }
    bannerView_.adUnitID = MY_BANNER_UNIT_ID;

    // Let the runtime know which UIViewController to restore after taking
    // the user wherever the ad goes and add it to the view hierarchy.
    bannerView_.rootViewController = self;
    [self.view addSubview:bannerView_];

    // Initiate a generic request to load it with an ad.
    [bannerView_ loadRequest:[GADRequest request]];
}
-(void)showAd:(NSString *)orient{
    // Create a view of the standard size at the top of the screen.
    // Available AdSize constants are explained in GADAdSize.h.

    if([orient isEqualToString:@"l"]){
    bannerView_ = [[GADBannerView alloc] initWithAdSize:kGADAdSizeSmartBannerLandscape];
    bannerView_.frame = CGRectMake(0,678,bannerView_.frame.size.width,bannerView_.frame.size.height);
    }else{
    bannerView_ = [[GADBannerView alloc] initWithAdSize:kGADAdSizeSmartBannerPortrait];
    bannerView_.frame = CGRectMake(0,934,bannerView_.frame.size.width,bannerView_.frame.size.height);
    }
    // Specify the ad unit ID.
    bannerView_.adUnitID = MY_BANNER_UNIT_ID;

    // Let the runtime know which UIViewController to restore after taking
    // the user wherever the ad goes and add it to the view hierarchy.
    bannerView_.rootViewController = self;
    [self.view addSubview:bannerView_];

    // Initiate a generic request to load it with an ad.
    [bannerView_ loadRequest:[GADRequest request]];
}
-(void)viewWillAppear:(BOOL)animated{
    [[NSNotificationCenter defaultCenter] addObserver:self  selector:@selector(orientationChanged:)  name:UIDeviceOrientationDidChangeNotification  object:nil];
}

- (void)orientationChanged:(NSNotification *)notification{
    [self adjustViewsForOrientation:[[UIApplication sharedApplication] statusBarOrientation]];
}
- (void) adjustViewsForOrientation:(UIInterfaceOrientation) orientation {
    [bannerView_ removeFromSuperview];
    if(orientation == UIInterfaceOrientationPortrait||orientation == UIInterfaceOrientationPortraitUpsideDown)

    {
        //load the portrait view
        [self showAd:@"p"];
    }
    else if([UIApplication sharedApplication].statusBarOrientation == UIInterfaceOrientationLandscapeLeft||[UIApplication sharedApplication].statusBarOrientation == UIInterfaceOrientationLandscapeRight)

    {
        //load the landscape view
        [self showAd:@"l"];

    }
}
-(void)viewDidDisappear:(BOOL)animated{
    [[NSNotificationCenter defaultCenter]removeObserver:self name:UIDeviceOrientationDidChangeNotification object:nil];
}
- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    return YES;
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}