define performance doc eligibility using Performance Document End Date in fast formula

Summary

Users are able to initiate performance docs after Document End Date has passed

Content

Our 2016 Mid-Year performance doc end date is set to 8/31/2016. The process is officially closed now.  However, users are able to initiate/create new forms after the end date passed. How can we prevent users from creating new forms now?

I've tried unchecking the Available to Use check box for the Document period.  However, completed documents disappear form the Performance page once the check box is unchecked.

I was advised to use a fast formula that refers to the Performance Document End Date.  Has anyone done something like this before?