sessions help - apache2 + mod_auth_ldap + PHP

Hello everyone! I am having some issues with authentication and was wondering if someone out there could point me in the right direction. I am using apache2 and have htaccess setup to require a valid user via mod_auth_ldap communicating with an ldap server. Everything works like a million bucks in terms of getting the user authenticated. The problems occur at logout. No matter what I do: destroying the session, overwriting cookies, creating new sesions, etc... I cannot get the system to require the user to re-authenticate using any method short of shutting and restarting the browser. Does anyone out there have experience with mod_auth_ldap and php getting the user logged out so that reauthentication is required when accessing the protected directories?? Thanks, th0th