If you have a low number of users, you could create a different session object for each page. Such as sessionHome, sessionNews, sessionBlog, etc.
Then, on page unload, set the value to TRUE. Then use a bit of code like this to give them a "Page Expired" notice if they try to return to that page:
Code:
<% If Session("sessionNews") = "True" %>
Warning: Page Expired. Please click here to treturn to the correct page.
<% End If %>
<% If NOT Session("sessionNews") = "True" %>
----- Display the normal page content -----
<% End If %>