Duplicate orders, customer being charged twice!!!

I am pretty sure that the cause of the duplicate orders are from customers double clicking or clicking twice on the last confirm order button.
I would like to put something on the last confirm page that says "please only click once" above that last button.
I'm not sure which page I would put that on checkout_confirmation.php or some other page and how to write in that text.

Any suggestion would be much appreciated.

I am presently using : v1.5.1
https://www.beadedpatterns.com

This has happened before, but only maybe once every couple of months and I just refund one of the orders.
I have had it happen 10 times this month and it is rather irritating, and a hassle to keep refunding orders.
It is random and it not happening on every order.