Track File activity on a Mac?

Hi,

I need to find a way of logging what files are accessed and copied from Macs on a network. Files on the sever are sensitive (for unreleased products etc) but the studio use freelance guys to do the work and they all need access. I just need to make sure they aren't saving files to a removable device or saving them in Dropbox or emailing them out of the network. Is there any logging software that can send me a report each day or alert me for every file copied off of a machine?

 

I'm even happy to add another device to the network that monitors all traffic etc.