hiding a topic from all but one segment (or list)

hiding a topic from all but one segment (or list)

My organization sends out a number of newsletters using Zoho Campaigns. One of those newsletters is for volunteers. In order to become a volunteer, a person has to first go through our volunteer orientation (training). After that, they can receive newsletters that inform them of upcoming volunteer opportunities. So far, so good.

But - there is a problem in that contacts in other segments who are assigned topics related to regular newsletters can click the manage topics, and assign themselves to the volunteer newsletter. They can theoretically now sign up for volunteer opportunities without going through our internal training.

So how do we prevent non-volunteer segments from seeing the volunteer topic in their topics management?