Why does it mention the flocks near the road?
Malbim: Sha'ul would never think to look for David there, for there are many shepherds there, and it is near the road, and not concealed. Therefore, Sha'ul entered alone without fear.
What is "Lehasech Es Raglav"?
Rashi: It is a bowel movement. Radak - Targum Yonasan (to do his needs) means so. One who is Mesech Es Raglav must immerse (before resuming Avodah in the Mikdash); one who urinates must wash his hands and feet (Yuma 3:2). Lehasech is from the root Nesech (which is poured), or Sichuch, for one who defecates covers himself, lest his skin be seen. 'Legs' is a euphemism for the anus. It is also a euphemism for the Ever from which urine leaves - "Meimei Ragleihem" (Melachim 2 18:27).
Radak: It is to urinate.
Why did Sha'ul seek David on the high rocks, but not in the cave?
Otzar Midrashim 1 (Alfa Beisa d'Ben Sira, after Tav): Hashem sent a spider 2 to rapidly make a web covering the entire entrance of the cave. Sha'ul was sure that if anyone had entered, the web would be torn.
Kli Yakar: Hashem removed Sha'ul's Chachmah in order to save David.
Malbim: David, in his Chachmah, realized that Sha'ul was sure that David and his men will hide the high rocks, and would never think to look for him in a cave near the public road.
Not all those Midrashim are reliable; I did not see another source for this. (PF)
Earlier, David had asked "why did You create wasps, spiders and lunatics? There is no benefit from them! Hashem said, do you belittle creations? You will need them! Regarding lunatics, refer to 21:14:2:1 and the note there. When David took the flask by Sha'ul (26:12), Avner would have caught him; Hashem sent a wasp to sting Avner, and saved David.
