A dupe preventer was badly needed, so I programmed it and stuck it on the various forms around the site. Tried and failed with javascript before, but now it's server-side. Before allowing the form to be processed, it checks the log to make sure an identical submission didn't just go through. Should work even if previous form didn't finish processing yet, which was the issue that kept previous dupe preventers from working (and causing the multiple forum posts with the same URL). Watching logs for false positives now. Hit me if anyone has any issues.
Probably a bit late now but this is how we disabled submit buttons, on submit, at the day job, to stop people making duplicate payments by double-clicking the "Make Payment" button.
Code in the image as UMD won't allow the HTML tags, click pic to see the code.
Basically it creates a javascript function to submit the form, and then when the button is clicked, it first disables itself, and then submits the form.