lock layer position?

I keep discovering that somewhere in the middle of video I have managed to bump the position of a layer, which makes me have to track down where it is and fix it.... Argghhh.

I have guides locked. I have disabled the arrow keys. But, I sometimes accidentally move a layer with my mouse. Sometimes means rarely. But, it only has to happen once to be a disaster.

All layers are meant to fit the composition size currently. Obviously, this won't always be the case. I can use fit to comp, once I find out where I have bumped the video. But, is there a way to lock the position so I can't accidentally bump it?

I am aware that I can avoid the problem by not bumping the layers. But, you can compare it to the idea of parachutes in airplanes. You can bring a parachute or learn not to have airplane accidents. But, the later choice is not prudent.

Thanks. Locking layers when not changing them seems like a good idea.