Layer Management > Lock (Manage Menu)

This command can be used to lock layers by identifying objects that are assigned to the desired layers. Locking a layer means to set the attribute "Lock", i.e. objects assigned to it can usually not be chosen and thus not be modified.

Choose the objects whose assigned layers are to be altered. Click on objects to choose them, including objects in locked layers.

After identifying the objects, their layer assignment is determined and all affected layers will be locked.