rainborick - 6:14 pm on Feb 7, 2008 (gmt 0)

The simplest and probably quickest methods would be to effectively remove significant content from the page, either by having it displayed via an external JavaScript file or through an <ifreame> that displays an HTML file with a "noindex" robots <meta> tag. This would leave the page unchanged for users, but make it very different for search engine robots.

Slowly starving the page of incoming links would be the other method, but it would be slow in many cases because it takes longer for a search engine to fully absorb a change in a page's link profile than it does to absorb a change in its content. This would have the advantage of being a bit easier to maintain some control over the drop, but either way will have some risk of incurring a deeper drop than you seem to want.