1)
What is the meaning of "Hisgartani"?
1.
Rashi citing Menachem: It is an expression of closure.
2.
Radak: This refers to Sha'ul. The Zifim told Sha'ul that they would hand me over to him. Since You did not want to do so, they were not able to!
2)
What is the meaning of "He'emadta va'Merchav Raglai"?
1.
Radak: From the confined place [of David and his men], You stood them in a spacious place. All this I will thank You when I am saved from them; I will not fear them any longer.
2.
Malbim: Refer to 31:8:3:2.