It would be nice to have a per-layer lock in order to prevent modifications to layers by tools like the move tool, which can operate on layers besides the one currently selected.

For instance, if you're placing objects on a map (with the map being a raster background) you might want to be able to quickly select the foreground layers (text or icons) with the move tool (and therefore not want to use the move tool's "move the active layer" setting) but will have difficulty if you accidentally click and drag the background layer by mistake. Doing this repeatedly and having to undo can cost a significant amount of time.

Turning the backround layer's visability off would work, except it's vital to placing the objects on top of it.

So, I propose an enhancement for the layers dialog that allows you to toggle a modification lock (similar to the way chains are currently toggled) per layer.