Stop form re-submission on back ?

[eluser]depthcharge[/eluser]
[quote author="junaids" date="1244342461"]can u explain this

Code:

$this->output->set_header('Cache: No-cache');

and where should this line be placed in code?

plus i have a different question...
when a user is logs in( submits username, password) to application...he is directed to his homepage. if he refreshes the page...username password is resubmitted and again authenticated..how can i stop this?[/quote]

When log in is successful do a re-direct to the users page, then if he refreshes he is refreshing the user page, not the form submit.

redirect is explained here