Sridhara Swami's Commentary
Duryodhana is factually telling Dronacarya that although Bhishmadeva is partial to the Pandavas, the Kaurava victory is dependent on the vigilant protection of Bhishmadeva. So he must be protected from all sides in such a way that he cannot be slain form any direction. The Kaurava army depends solely on the might of Bhishmadeva.