I cannot get the back rotor off

Rear wheels are more suseptible to corrosion than are the front. A corrosion ring forms between the brake rotor and the wheel hub assembly. Use a large rubber mallet or a baby sledge to hit along the top edge of the rotor in order to break the corrosion ring. Some care may be needed if you are trying to re-use the rotor after they are turned down, otherwise you can hit the rotor much harder, and they should break free.

If not, apply some heat to the seam area between the rotor and hub. It will smoke, but do not get it red hot. Remove the heat and try using the hammer once again. Be careful not to grab the hot portion of the rotor when it breaks free.