DLP Endpoint Prevent and Zip Files

I may have found a gap in the DLP EP Prevent that I need help closing.

Use Case:

Say I add sensitive data to an excel spread sheet. I then exit excel and go into Windows Explorer and right click on the file and select add to archive/zip and when lets say 7Zip option open and I select to give the file a password then zip and I email the zipped password protected file DLP will not see it.

Any ideas (I am sure it's that I havent thought of one) other than creating a policy to look for password protected files?