LockDock

I wrote a little Mac App for locking/unlocking the Dock against changes of any kind. It asks for admin-rights when run, so it can't be tampered with easily. It should work from OS X 10.4 on, I have only tested it with 10.7 Lion.

Download: LockDock 

It works by using calling the following shell commands (via applescript)

defaults write com.apple.Dock contents-immutable -bool yes            

defaults write com.apple.Dock size-immutable -bool yes            

defaults write com.apple.Dock position-immutable -bool yes

killall Dock

(or replace yes by false for unlocking)

Send me a message if you want the XCode project...