Lock keyboard for Uni Exhibition/show

I have a macbook which i want to lock just the keyboard/mousepad so i can leave my laptop (which will be cable locked to a display stand) running a CAD program preview on.

I dont want the screen to go off (so counts screensavers out) and ideally want to be able to enter/hold a combination of keys to lock/unlock the keyboard so people do not mess with the computer while i am not there.

Any ideas what software is available (keyboard cleaner is the closest but shows the passcode/combination so is no use).

Cheers Ben

Hi. This may be of use to you:

How to lock your Mac with a keyboard shortcut : Switching To Mac

Or this:

System pref> keyboard and mouse> keyboard shortcuts> select, turn off keyboard access. F1

Better option would be to find a separate monitor, and then keep the laptop closed and under the stand so that people don't try messing with it.