Custom Module Input Form - Preventing Another Submission after Back Button

I am using a custom module to track member votes for an election. I have a custom module input form. On page load it checks to see if the secure zone user has already already has a custom module item. If so, it hides the form and show the user their previous vote.

However, users are clicking the back button and voting twice.

Any suggestions to prevent this from happening?

Here’s a Stack Overflow article that has a variety of possible solutions:
ajax - How do I detect if a user has got to a page using the back button? - Stack Overflow
But it does seem like browser compatibility could be an issue for many of these.

Alternatively, you may be able to disable the back button altogether:
How can I stop the browser back button using JavaScript? - Stack Overflow