To avoid inadvertently making changes to items on a layer, you can use the Layers palette to lock the entire layer.

Layer locking is independent from item locking. Items locked using Item > Lock can still be selected and edited; items on a locked layer cannot be selected at all. If you lock an item on a layer using Item > Lock, and then lock and unlock the layer, the item retains the item lock even after the layer is unlocked.

The Lock column in the Layers palette controls the locking of layers. To lock layers, use one of the following methods:

• To lock or unlock a layer, click in the Lock column to the left of the layer’s name. You can also double-click the layer to display its Attributes dialog box, check or uncheck Locked, and then click OK.
• To lock all but one layer, press Command/Ctrl and click in the Lock column next to the layer you want to edit.
• To lock all layers, choose Lock All Layers from the palette menu.