How to create user friendly pop-under ads

I just came back from a quick vacation in Munich, and on the train I wrote a small introduction to pop-under ads for a friend. Personally I am not a friend of ads, pop-up or pop-under, but sometimes you need them.
The main problem I have seen so far is that bad implementations cover the content even when JavaScript is disabled, thus making it impossible for the user to get rid of them.

This article describes how to create user friendly pop-under ads with CSS and DOM and offers an example that only covers the main content and gets a “close” functionality when the browser allows it.

Hopefully you’ll find it helpful.