 Why would the Furry Ones not follow Rolf and the others when the retreated?
Sisko Rolf's stocky body was a blur of motion as he cut the rocket jets, doused the twin searchlights, and switched over to the audio beams that served so well on the surface when blind flying was in order. "Trapped us neatly," Rolf said through clenched teeth. Rolf swung the lax controls over hard as the bursts of fire revealed a looming barrier of stone dead ahead, and then he felt the tough skin of the flyer crumple inward. Somehow Rolf found the strength to wrap his fingers around the control levers and snap on a quick burst from the landing rockets. Their mad speed checked momentarily, but the nose of the vertically plunging ship dissolved into an inferno of flame. Without water and food certain death grinned in his face, for beyond the sand-buried entrance to these lost equatorial caves there were no pressure domes for hundreds of miles. Here at least the air was thick enough to support life, and somewhere nearby the outlaws who smuggled their precious contraband water into the water-starved domes of North Mars lay hidden. How many hours later it was when the first faint glow of white light reached his eyes Rolf did not know—it had seemed an eternity of endless plodding along that smooth-floored descending tunnel. "They may have found the sunken seas of Mars," thought Rolf as he moved alertly forward, "water that would give the mining domes new life." As the spinner dropped him slowly down into the vast emptiness of the great shining gulf, Rolf could see that a broad band of stone divided the green fertile plains and forests from the desolate desert wastes of the other half. Toward this barrier the spinner bore him, and Rolf was content to let it move in that direction—from the heights of the wall he could scout out the country beyond. The spinner had slowed its speed; it seemed to Rolf that he must be falling free in space for a time, but the feeble gravity of the tiny world tugged at him more strongly as he neared the wall. And the barrier became a jumbled mass of roughly-dressed stone slabs, from whose earth-filled crevices sprouted green life. So slowly was the spinner dropping that the blackened desolation of the other hemisphere came sliding up beneath his boots. Deftly Rolf nested the spinners again in their pack before he set out toward the heaped-up mass of stone blocks that was the wall. Ten steps he took before an excited voice called out shrilly from the rocks ahead. "Sorry," said the tall man as Rolf sprang easily from the ground to their side.
 They feared the Ancients.
 They had lost too many to continue fighting.  They were warned not to by Altha.  They feared the Ancients.  They knew they were losing the battle.