You will probably have to replace the rear rotors. The parking brake is a drum brake inside the hat of the rear rotors. The problem is, if you don't use your parking brake frequently the shoe gets out of line and then wears a groove into the drum surface.
Its hard to explain but because of the groove, you can't get the rotor over the parking brake shoe and then have enough adjustment to get the parking brake to hold. I was never able to find anyone that could turn the inside of the rotor. New rotors were only about $35 each if I recall.
I ended up replacing the parking brake shoes, rotors and new pads since I got new rotors. Once you fix it just remember to set your parking brake every night. It recenters the shoe in the drum and will greatly lessen the chance this will happen again.