Saul encamped in the hill of Hachilah, which is before the desert, by the way. But David abode in the wilderness, and he saw that Saul came after him into the wilderness.
So David is sort of chiding Abner the chief general of Saul, saying, "Hey you know your job is to guard the king, and you aren't doing a good job. You ought to be put to death. Someone came in to destroy the king, and you were just sound asleep. Look where the king's spear is, and the cruse of water."