It's my understand that Adsense doesn't approve of an ad being hidden behind another layer. So with that in mind...
On tablets and mobile devices, I'm showing locally-sold ads using a simply:
I want the locally-sold ad (NOT the Adsense banner) to stay fixed on the bottom of the viewport while the user scrolls up and down. But I also have 728x90 (tablets) or 300x50 (mobile) Adsense banners that will scroll with the page, and I have to worry that them scrolling behind the local ad will be a violation.
If that's true, what's a smart way to accomplish this without violating Adsense policies?