I Sealed the Shelter

I made the Shelter a private node. I was looking through forum permissions, and saw that The Shelter wasn't checked as a private node, and made it one. See, if it's not made a private node, but is hidden, that keeps people from seeing it via the list. If, however, they remember the URL to the forum, they can still view it. By making it a private node, they will not see it unless they have explicit permissions.

So before this people could have accessed the Shelter even without permission to?

Yep. As long as they could see the shelter URL or someone tell them the URL, and they would have been able to view everything in it.

Done.