Is there a way, once a form is submitted, they cannot hit the "back" button and resend the same form again and again?

It's possible to limit submissions on your form, please check the guides below that will help you doing so: 

https://www.jotform.com/help/64-How-to-Set-Unique-Submissions-on-a-Form

https://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question 

I hope this helps. 

I made the changes to "cookies only." The problem is this is a form that needs to be submitted daily. This change prevents the form from being sent again. I need the form to be "emptied" of the answers, once the form is submitted. Preventing employees from hitting the back arrow, and re-submitting the form, without repopulating it, again the next day.

This is something that is controlled by the browser itself. The previous page state is saved by the browser, so we cannot affect the back button behavior.

However, it seems to be working differently when the form is embedded with a standard JS embed code: Adding a Form to a Web Page

When the JS embed code is used, the form appears to be not loading back in Chrome, Safari, Internet Explorer and Opera, it is still loading in Firefox though.