Logoff and Browser Back Button Issue

Ok so I'm currently upgrading my website and I want to add logon and logoff functionality. I've successfully added the logon part and I created a link that redirects the user to the main page (logoff). The issue is that after the user logs off he/she can just hit the back button and be logged in again. I dont want to disable the back button because realistically you can't disable the back button you can only make it more difficult for the user to use it. To me disabling the back button is not an elegant solution. I've also tried javascript and I went around it by simply disabling javascript. If anyone has a real solution please let me know. Thank you.