This is more for people like me, who were looking for a solution and stumbled upon this conversation. (I assume the original poster's problem has long been solved.)
The only easy solution I've found that worked (not saying there aren't any other solutions - I stopped looking once I found this one) was to use Wise Folder Hider, which is free. It sets a master password and hides the folder you wish to make inaccessible so that even Windows can't see it. In order to again be able to access that folder, you then need to open the Wise Folder Hider program, which can only be opened using the aforementioned password. (Of course, some more knowledgeable users will find other ways, but I couldn't find an obvious one, and that was all I needed.)