Setting up submission limits of a form so that submissions are made once per person

My next step is to decide on loose vs strict submission controls vs trusting the voters to vote only once. As it sits this form is anonymous and everyone can vote secretly but there's no way to prevent multiple votes.  

I want to prevent stuffing the ballot box. Can strict controls be enabled with a generated token instead of forwarding the name or email address to us? Something that would store the data but not necessarily share it with us? Do I hide those fields from the confirmations and let the voter think they're being anonymous and live with it?

Loose control would work with just IP address capture assuming people didn't vote at work, at home and on their phone. 

I am not truly worried about the group doing this, but having the systems in place prevents grousing, finger pointing and general discontentment. It's also a good thing to learn for other forms

Based on what you have mentioned, neither cookies nor IP check will work if someone goes back to the form from outside of the office.

Now what you could do is the Unique question check.

Now that would mean that one "key" can only be used once.

Since these are your colleagues, I think that it might be fun to pull these numbers out of hat.

That way you can capture the unique ID and in the same time not know who exactly submitted that form. So you are not able to tell who they are and they are not able to cheat it.

You can see more about this here: http://www.jotform.com/help/223-How-to-set-Form-Limits-Based-on-a-Unique-Question

Alternatively, if there is some zone where your employees can access only from the office and this has access to internet, you could embed the form in that location and have it submitted from there.

Hope these spark an idea or is something that you can do.