U will not see your layer border beacouse u are cuting off it with ur layer mask. It's why u see only fragment of it and other not. They are cut.
The best way to do it is to creat a graphic for the buttons and replace bacgroundimage for example:
icon = [UIImage imageNamed:@"name"];
[Button setBackgroundImage:icon forState:UIControlStateNormal];
U can set for other state to like: UIControlStateSelected some other image.