Hello Hans,

The only way you have to protect your pages is to use a Private Area.

If I got it right, you would like to protect a level wich contains more pages. If so, you should:

1. Protect each page contained in that level.
2. Go to step 2 and show the level's properties. 
3. In the level's properties, select "Dont' show the submenu of this level".
4. In the level's properties select "Link on click for this level" and link the first page contained in the level to the level itself.
5. Activate a page menu to allow the navigation in the private area.

That's it!