That's the enrolment plug-in, so if they are in a Program and access the course - they're enrolled.

What Daniel was suggesting was to add a new enrolment instance of Audience-sync, and then add your audiences that are in the program that way - this means they'll be enrolled before accessing the course.

If you're not using audiences to enrol into the Program, then create a new audience where the Rules include "Program assignment" and select your Program/s.