As an admin user you can make all future deficiency list items private by default. To do so, click on the 'Configure Deficiency List Settings' in the bottom right of the Deficiency List log page. From this page select the 'Deficiency List Items Private by Default' checkbox. See Configure Advanced Settings: Deficiency List.
This will make all future deficiency list items private, but will NOT retroactively mark existing deficiency list items as private. If you want your deficiency list items to be private, we recommend you do this at the beginning of a project.
Private deficiency list items can only be seen by 'Admin' level users on the Deficiency List tool and those included on the item.