loging out with session.Abandon()

i was thinking of having a hyperlink which would log the user out. currently iam using a session object to log people in, ie session("permission") = true and then checking this on every page. i was woundering how i make a link run a script which sets session("permission") = false. but for some reason the user is only logged out out of every page only if they double refresh the page, otherwise the page detects the person as loged in. i think i need to set some cache to something. can anybody help? thanx in advance.

you're a bit vague about the actual situation where users can see earlier pages.

I assume they browse through the history?

In every case: sounds indeed like caching problem. Here's a recent thread about trying to prevent clientside caching
http://www.codingforums.com/showthread.php?t=41607