How do we lock the new Mac Pro down in a lab?

+1 to what Grant said.

Though it's not all that elegant, I'd consider looking into a thin airline cable. Airline cable is a thin twisted-strand cable that's flexible and incredibly strong. Slot it through the aluminum air vents in the base, then you can secure the cable whereve you like. Perhaps, in the weeks and months ahead, we'll see a third party vendor offer up a solution.

My guess is a slender cable through the slots in the base. If you are in a really tough neighborhood, a hole drilled in the center of the base and a large bolt through the base and through the benchtop.

See what I found !!! Seems maclocks has just intreduced the world's first New Mac Pro Lock :

http://www.maclocks.com/mac-locks-macbook-pro-lock-macbook-air-lock-macbook-pro- retina-lock.html

This is how I found it:

http://reviews.cnet.com/8301-13727_7-57617913-263/maclocks-announces-security-lo ck-for-2013-mac-pro/

There is no security lock on the Mac "Pro" as with all prior models. You will have to lock it in a well ventilated cabinet.

Here's another option for a Mac Pro Lock.