“Logout” after Logging In

I require users to log in to see my blog. If a user closes their browser, I want them to “log in” again. Since I change the passwords every month, I don’t want people with “old user names and passwords” to be able to authenticate. I remove their name, but if they didn’t log out, they can still access the content.

I guesss some sort of a time out feature.

thanks in advance for you time.
Josh