Best way to disable going back to form page after user has clicked submit?

[eluser]Unknown[/eluser]
Thanks for your reply =)

Although I've tried the code mentioned in that topic:

header("Expires: Tue, 01 Jan 2000 00:00:00 GMT");
header("Last-Modified: " . gmdate("D, d M Y H:i") . " GMT");
header("Cache-Control: no-store, no-cache, must-revalidate, max-age=0");
header("Cache-Control: post-check=0, pre-check=0", false);
header("Pragma: no-cache");

But the cached "survey form" page is still being displayed after clicking the back button upon viewing the "thank you" page.

What I've noticed the above code does do though is:

If the user fills out the survey, misses 1 or more questions, my validation is run, the page is reloaded with the "Please select an answer!" error message beside each question they've missed, user then fills out the missed field/s, clicks submit, see's the "thank you" page. NOW if the user clicks back, (which would take them to the form with error messages) the "This page has expired" error displays (which is good!) however if the user then clicks back again - they are brought back to the original survey form page.

It's really stressing me out! haha any other suggestions?