Mose secure way of checking Product ID and making mysql updates on checkout.

[Leathel]

Trying to see what would be the most secure way of doing a query on a specific product id on checkout, then if that product id, run a mysql update. I've tested the code on the checkout_success.php and get the desired results, but not sure if the code should be placed in a certain area of the page so somebody can't just keep hitting refresh. Or if there was a better/secure way of trying to achieve what I am looking for.