One word of warning: It's not unknown for cables to be buried only
just below the plaster on some walls, particularly old places which have been rewired more recently. (Yes, our recommended electrical codes say that the cables should be either at least 2 inches below the surface or protected with a metal plate, but that doesn't always happen.

).
It's best to avoid nailing anything either directly above, below, or horizontally in line with any outlet, wall light, or switch, if possible.