Shortly after Dumbledore left, a figure materialized out of thin air without warning. Raising his wand in vigilance, he swept his gaze across the destroyed house ahead, then checked the watch on his wrist. Satisfied that no one else was around, he slowly lowered his wand and walked toward the entrance of the underground chamber beneath the ruins.
The Ministry of Magic's Aurors had failed to breach the chamber—or rather, they had been blocked by the defensive measures left behind by Voldemort. Clearly, they would need to summon a more specialized spell-breaking team to crack Voldemort's dangerous curses and the hidden entrance.
As for leaving someone behind to stand guard?
Chapter 1031