Preventing copper wire theft

[Jeff Sheraton]

Does anyone have any creative ideas to prevent copper wire theft?  

We have had a few houses get hit (always while they are vacant).  Thieves will steal copper plumbing and wires.  We always replace plumbing with pex, but we do not have an alternative for the wiring.   

I've considered making something to prevent the electric from being turned off (for use while the houses are vacant), but this seems like a pretty big hazard/liability.