1)
Why did he say "l'Oyvei David"?
1.
Radak: This is a euphemism for himself. (He did not want to mention something bad happening to himself.)
2.
Kli Yakar citing Mahari: If I do not totally destroy Naval's house, Hashem should give to my enemies wealth like He gave to Naval.
3.
Kli Yakar: Hashem should do to my other enemies like I do to Naval - if I leave a remnant, He should leave a remnant, and if I do not, He should not.
2)
What is "Mashtin b'Kir"?
1.
Targum Yonasan: It is one with knowledge. Rashi - the words hint to Meshis (puts, i.e. thoughts) b'Kiros Libo (in the walls of his heart).
2.
Rashi citing Yerushalmi Sanhedrin 2:3: Even a dog, which normally urinates by a wall.
