Well no other front did present a continuous stone wall with such an heavy military presence. Simply look at the forces deployed on the wall vs the lenght of the defended border, and add to that the three supporting legion further south, and then compare it with the density of troops on the German border (which used waterways and a berm + wooden wall with observation towers and camps as defense), the Danubian border (water + towers and camps), the desert border (fortlets and bases) or the Algerian side (unguarded low wall to direct traffic + fortresses) : you do indeed have the most heavily guarded border. You may want to check David J. Breeze's book "the frontiers of imperial Rome" (Pen & Swords 2011), for example figures 17, 20 and 22 :