Exactly what Cinder said. I did that with one of my dogs when we got her quite some time ago. She's a rottweiler too!

I sat out there forEVER!!! waiting for her to go. I took her to the same spot and gave her much appraisal after she did her business out there. Then I took her off leash after a while of doing this with her, she'd go do her business in that one spot then come running to me, expecting a treat. (that was part of the appraisal.) It used to take her thirty minutes, then it gradually went down. To this day, she still only does her business in that one spot.