Copy Protection For General Files

I'm making a program to protect custom game files from being copied as best I can, however there are a couple things I need to account for. Some of them I have, others, I have not been able to find information on. When the files are not in use, I have them fully encrypted and hidden from the lay user through a bunch of other tricks (+s attribute, for example). However, I would also like to prevent copying these files while they are being used by the game - obviously I cannot have them encrypted while the game is attempting to read from them.

This opens up a hole, which I have also tried to deal with, but I know my attempts in this regard are less than thorough:
Stop several known well-known copy programs from operating during operation, that being Windows Explorer, Teracopy, and cmd

Now, the other solution I was thinking of was a filesystemwatcher object scanning the better part of the computer for any copies of these files located outside of the "OK" directory, but I'm a bit skeptical as to whether or not this would be very efficient. Any ways to make copying these files difficult without rendering them unusable to the program.