Sync specific folders to file server on logoff

Hello

I have 20 users joined to active directory version 2008.  I want some specific folders (ex. c:\my.files ) to automatically be synced with my fileserver (for backup purposes), when my users logoff or shutdown their computers, .

I am thinking to create a batch file which simply xcopy these folders to my fileserver using logoff scripts in group policy.

Is there any other way to do?  What if i want to sync files and not copy all data every time a user logoff/shutdown?

Thanks