Ask HN: What Is an “Water Tower Ad” Equivalent on the Web?

A water tower is highly visible to anyone nearby and will be around for 50 or more years. If you own the tower or its advertising space then you have permanence. This is hard to beat with technology unless you are Google, Microsoft or IBM.

Fifteen year old adverts are about as permanent as you get: http://www.milliondollarhomepage.com/

A look at the page shows that long term ads are not as useful as they first seem.

Other than that, a short .com domain name can be used to permanently advertise whatever you want if you can afford to buy one.

Other than that, find a popular website and make them a deal. You advert will last as long as your credit card and the website. In reality that's isn't forever.