Do not allow user to view page using browser back button

 

// We never want the user to get back to this page via browser back

 

// so prevent this from happening

Response.Cache.SetCacheability(HttpCacheability.NoCache);

There is also MS KB article, that shows How to retain only the most recent Web page state in the Web browser history folder.

The latest (still in Beta) ASP.NET AJAX has  ASP.NET 3.5 Extensions History Control Tip