You can protect an item in your tree from accidental deletion or from being changed. To prevent deletion apply a lock. This will not prevent the item from being edited and changed.
To protect the contents of an item make it read only. This prevents the item from being overwritten by a changed version but does not prevent the item from being deleted. Should a user attempt to delete the item a warning box is presented indicating the item is read only and asking the user to confirm deletion.
Open the properties of the item.
Select the General Tab
Check the box for "Read Only".
To make all children below the item read only also check the "Apply read only setting to sub items" box.