Chances of having a sucessful vba2c?

First birth was an emergencies c-section due to baby having birth defects and didn't make it back in Feb. 2009. Second birth was repeat c-section at 37 weeks. Baby healthy in July 2010. This pregnancy is healthy and the baby is due September 2 of this year. What is the percentage of uterine rupture in this situation? If a do not want a c-section can they make me have one legally? What could the doctor do? What should I do if the doctor insist on making me have another c-section?