How to lock a layer in After Effects and still be able to edit it

I have been working with After Effects to modify a film clip that needed an animated mask to hide part of the image. However, every once in a while I would select the layer by accident and move it--which if you don't catch your mistake immediately, messes up your entire animation. Anyway, a bit of Googling and I found this brilliant (and simple solution here):

http://generalspecialist.com/2008/03/locking-after-effects-layers-so-they.asp

The short version is to select the layer in question, open the expressions panel for the "position" property and place the current position of the layer in brackets like this [123,23]. This simple script resets the position of the layer back to the original every time you mistakenly move it. BRILLIANT!