1)
What is the meaning of "Ein Naki"?
1.
Rashi (from Sotah 10a): Even a Chasan from his room [of seclusion with his Kalah], about whom it says "Naki Yihyeh l'Veiso Shanah Achas" (Devarim 24:5; even he is not exempt from this).
2)
Why did he build Geva and Mitzpah?
1.
Malbim (Divrei ha'Yamim II, 16:6): These were fortified cities to stop enemies; Geva was near Ramah (Shoftim 19:13), and it says "Pach Heyisem l'Mitzpah" (Hoshe'a 5:1), for also it was near Ramah, where [Basha] tried to stop traffic to and from Yehudah.
