Is there a way to protect PHP's $_POST, $_GET when user tamper with post string in URL toolbox???

Hi! I wanted to know is is there a way to configure PHP to make it not be affected when the web user tamper with the values in the post string after a webpage is submitted or something. (Further explanation below) I noticed when I use the hidden html input tag with hidden data in it then when I click the submit button to submit the webpage, the hidden data then show up in the URL address. Fine, no problem. But I noticed one problem, I can changed the value in the URL toolbar of the web-browser and get different result on the webpage. I know it is where $_REQUEST[], $_GET, etc. come into play. So, is there a way to keep that $_REQUEST[], $_GET[] data unchanged? Does this require the php.ini configuration or what? Thanks, FletchSOD