Last week at the SEMNE event in Rhode Island, Jill Whalen reported that Google introduced a new META tag. The impact could be far reaching for SEO's and marketers in many industries - ecommerce, affiliate and beyond.

The "unavailable_after" tag will allow websites to notify Google that a particular page will not be available for crawling after a certain date. If you are using special offers that expire or have content that was free and is now behind a subscription wall for example, the META tag is a good way to let the search engine know that the page should no longer be indexed.

Unfortunately for those that want to implement this on their own sites, their is little in the way of information on the proper syntax of the tag - so there will be a lot of discussion on how to validate the code in the future. Until there is a formal announcement from Google however, you may just want to try another method, commonly called the "410 Gone" - an HTTP status code.

If you simply want to inform Google (or any search engine) that a page has been removed,  the "410 Gone" status code indicates to the spider/bot that the requested resource is no longer available at the server and no forwarding address was provided (source - W3.org). The 410 response assists in the process of web maintenance by notifying the recipient that the resource is intentionally unavailable and that the server owners desire that remote links to that resource be removed. Such an event is common for limited-time, promotional services (e.g. affiliate programs).