Create a new section (admin > setup > section) and assign it to your new content. I think that this, in itself, should be enough to meet your requirements.
You can get a lot more complex with it, but if you create a new section and don't explicitly give the anonymous role permission to see it, admins will be able to see it when they are logged in.
To be safe, you can also create a new role which has access to content/read/yournewsection and apply that (along with the anonymous) role to new a user group. Then add users to that new group and they will be able to see it. Do this if the people who you want to see the new hidden folder really are not admins.
The way you were trying to do it would be appropriate if you wanted content to be visible on the site, but not as a direct link from the navigation. You could exclude a particular node from flat_top.tpl to make that happen. But the content would still be visible in search and by direct link.