How do I re-hide exposed hidden and erased items in terminal

I am a professional photographer and a few weeks back delivered a hard drive with several hundred gigabytes of photo selects, all in one folder, to a client. There was another folder filled with outtakes on the hard drive that I erased.

Later, I was surprised to discover they had retrieved the outtakes and were putting them to uses I had not authorized.

I was wondering how they did this, plugged another hard drive with deleted material on it into my iMac 27 inch OS X El Capitan, got online and found instructions for showing hidden files using Terminal. I tried it, and it worked. I learned something important but also created and new and aggravating problem for me.

Now, I cannot re-hide hidden and deleted items. They all show. I have looked for the answer with Google but I cannot find it. Please help.