Browser Back Button and Strange Form Behavior
In my application, a user visits a website to "request" a form by email (this insures he owns the email address by the way..nice trick). When he submits this stateless from (his name and email), a random number is generated and added into a new "blank" entry on the ZC database. When he opens his email, and clicks the link, the link is keyed to open the new blank form using the aforementioned random number. He then fills out the form, and clicks submit. The code reloads the page with a thank you message. Behind the scenes, script updates the ZC database entry with a new random number key. This was to insure the original requested link by the user can only be used once. HOWEVER, if the user clicks the Back Button on the browser, the form is still there even though the script changed the random number key! How can this be? Also, it seems all the code built into the form (ie field validation etc) is 100% operational AND he can submit the form again to make a new entry.
How can I ensure a link to a form only works once?
PS: I'm using private applications so all my links have the very long private key string.