Problem with j_security_check

I've got this problem.
I'm using j_security_check for autheticating users with a form based login.
The login and logout work, but I want on thing to work and i can't seem to work it out.

When I use the back button from the browser after I logged in I see the login screen again (sounds normal) but obviously I didn't logout.
When I try to login again Tomcat gives an error that I'm already logged in.
I tried to create a JSP page that checks for a session object (if there is a session object it's gonna be removed, if not just go on) but when I try to forward the page again with the login parameters from the login form i get an error that j_security_check can't be called directly.

I know why Tomcat gives these errors, but I can't find the solution to this.

If anybody knows how to solve this problem please post something because it drives me crazy.

Thanx in advance.