1)
How is Hashem a hiding place and shield for him?
1.
Radak: He stops those who want to harm him from doing so.
2.
Malbim: I do not fear evildoers, for You hide me, so they do not see me. And if they approach me, You shield me from them.
2)
What is "Devarecha"?
1.
Radak #1, Malbim: Your promise.
2.
Radak #2: Your Torah. One who guards it, evil will not come to him.