>First, thank you for the sample code. As I mentioned to Viv, when user submits an order, the Acknowledgment is shown. And it clearly says that the order has been received. But users, for whatever reason, can click on Back button (in the browser) and return right back to the Order page. The order page "does not know" that this is a duplicate order and user can Submit it again.

As is, you can implement something I have here on the site. This is in regards to how the messages are posted. Before, in the earlier years, we had some of that. So, what I did was to verify for the same content posted in the last 10 minutes for example. To that, you can add the IP recognition and ask the user if he or she really wants to submit the order, that would assume you would be pretty sure they are about to submit the same. In that case, you would ask for a confirmation before the final post.

You can also establish an automatic expiration of the previous page. So, once the back button is pressed, it will go nowhere.