Deny access to copy files

I am working for a software house, they are developing a software product
and their requirement is to restrict programmers to take the code out of
office premises due to company policy. I am trying to configure a windows
based machine which denies access to copy files to external storage devices
connected to USB. There is an NTFS permission “Read + Execute” I guess this
could do the work but is there any other way to do it? 

They also don’t need programmers to take the code with them in their email.
I can restrict SMTP and POP ports but when it comes to web based emails I am
clueless,  How can I restrict web based emails like hotmail, gmail, yahoo
there are so many of these and if I somehow manage to block all web based
email sites someone can write a script to send emails, if not a script HTTP
tunneling would bypass any checks and bounds defined by my proxy/gateway
machine. How can I block such thing?

Any help would be highly appreciated.

Regards,
Ahmed Khalid