OS X :: Preventing File Copying For Security Purpose

I have a bunch of highly confidential business files, to which I need to provide one of the staff in my office access. I do trust the person, otherwise I wouldn't think about providing them access in the first place, but as a security measure, are any of the following possible?

- Preventing the possibility of being able to copy and paste the file from Finder into a USB key. I need the file to be readable and writable, but would like to make sure it does not leave my computer.
- Logging a user's activity. I've looked into parental controls, and I've looked into the Console, but one is too limited (sites only) and Console is too complicated. I want to have a quick overview of what's going on. Simply put, I probably will never look at this log, unless that staff member leaves the company.