I tried removing the rear rotors the other day only to find that they were held on the hub by something I couldn't see. Turns out that the ebrake on our cars is actually a drum brake and the shoes wear a little lip on the inside of the rotors. If you don't back the shoes off, the rotor won't pop off. If you look on the inside of the dust cover, you will find a small oblong rubber plug. Remove that plug and you have an access hole to a gear on a rod. Using a flathead screwdriver, turn the gear teeth upward to retract the shoes (there is an arrow to remind you next to the hole).