Can OS X be remotely accessed using the GUI but securely to hide what is displayed locally? The remote screen sharing feature of OS X is extremely convenient.  I can access my office machine from home when I need some software that can only be installed on on-campus computers.

However, I noticed that if I log in to the office machine through screen sharing, everything I see on the shared screen is also mirrored on the machine's physical screen. Logging in using screen sharing unlocks the machine's physical keyboard and mouse as well.

Is it possible to avoid this security risk if someone can see or manipulate my Mac while I am not in the office?  

Is it possible to access a remote computer through a graphical interface (not terminal) without exposing directly that machine to anyone who is in the office at that time? Of course they could steal the machine, but I don't want them snooping on grades or email or whatever when I unlock the screen remotely to access the Mac.
Yes - there are several ways around this. 

The free, but less elegant solution is to make a second account on the Mac you wish to keep private. Set the machine to boot to that user and use Fast User switching to switch to your account. 

Then when you log in - it will ask if you want to share the dummy account's screen or make a second virtual (and not drawn on the monitor) screen.

Alternatively, buy Apple Remote Desktop and use the "curtain mode" where it obscures the screen to hide what the remote operator is doing.