Locking layers
You can create complex drawings as a series of layers. As you complete each part of the drawing you can lock the layer (make it non-editable). This ensures you cannot accidentally move objects. When a layer is editable, objects on it can be selected and edited. If you try to click on an object on a non-editable layer the click will pass straight through it as if it was not there. Even Select All will only select object in visible, editable layers.
To lock layers
1. From the Utilities menu, choose Layer Gallery to open the Layer Gallery.
2. In the columns next to the layer name, click the right-hand check box to swap the layer between locked and editable.
Tips
You can make all layers editable temporarily by clicking the All Layers Editable button at the top of the gallery. Clicking it again sets all the layers back to their previous state.
The current layer (the one highlighted in the Layer Gallery) can be forced to always be editable and visible (see General Options).
The editable setting for a layer can also be set by right-clicking on the Layer Gallery and choosing Properties.
To make a sequence of layers editable, set the first to editable and Shift-click on the last. The editable setting of all the layers in between change too.