you can lock a folder and make it so that you can only add files but cant open it. to do this go into get info on the folder then at the bottom lock it put in your system password. to unlock it do the same. the folder becomes a drop box, you can add files to it by dragging it in but you cant open it unless you unlock it. someone correct me if i'm wrong on the exact process since i'm at work and not in front of my mac right now.