More detailed informations to check:
Is magnesium electrolysis in water possible? Do you know a condition for a metal to deposit from an aqueous solution?
Do copper electrodes participate in electrolysis? There is one known example with sulphate. Is copper a good choice at all?
What are typical voltages for electrolysis? Hint: they resemble one-cell battery voltages, since both result from the same values. Do 9V single-cells exist?