In the latest edition of The Oldie I recommmended a useful little widget called Lock-a-folder, which is supposed to put passwords on individual foldres.
It's a good idea, but it seems that the latest version (not the one I tested) has some bugs in it, so PLEASE DO NOT TRY IT until I am satisfied that it is corrected.
I will post a note here when the coast is clear.
I'm very sorry if you've been caught out by this - it's very irritating.