Why did he say "Yashuvu la'Erev"?
Rashi: These Resha'im, what they do during the day is not enough for them. Also at night, they return to their evil, to guard me, lest I flee.
Malbim: [After trying to kill me during the day, Sha'ul] returns at night to send guards around the house to kill me.
What is the comparison to a dog?
Radak #1: Just like a dog barks at night, so they howl when they are awake at night [guarding] me.
Radak #2: Refer to 59:7:3:3.
Malbim: They guard the house like dogs do, and howl like them.
Why did he say "Yesovevu Ir"?
Radak #1: They surround the house for David (to ensure that he not flee).
Radak #2: Perhaps Sha'ul sent additional men to go around the city, so if David will escape those who surround the house, those who surround the city will catch him.
Radak #2: Just like dogs surround the city, so they surround the house.
