Does anyone know of any software or way that allows me to lock/freeze any application/window on my screen
i.e. disable any change in position and size / make it completely immune to the cursor or clicking?

I'm running an application called LiveSplit, which is a timer. It always stays on top while I'm playing a game, which is a good thing, but sometimes my cursor accidentally clicks on it and then all hell breaks loose. I end up accidentally moving and resizing the window and it becomes a mess.