Why did he say that Hashem is a shield for him?
Radak: This is unlike their words, that he has no hope in this world, and not in the world to come. So they think and say; You will do oppositely, and be a shield for me in this world and in the world to come. "Magen" applies both to "Ba'adi" and to "Kevodi".
Malbim: This answers those who contest [only] his kingship.
What is "Kevodi"?
Radak #1: It is the Nefesh, like "va'Yagel Kevodi" (16:9), "Lema'an Yezamercha Kavod" (30:13).
Radak #2: [It is my honor -] the opposite of his disgrace when he fled.
Why did he say "u'Merim Roshi"?
Radak: I will not be ashamed, and my face will not fall in front of my enemies. Rather, I will go upright with my head lifted. When You save me, they will recognize and know that You pardoned the sin through this punishment that You punished me.
Malbim: This answers those who say that Hashem will not save him, due to his sin. You are my honor, and lift my head. My honor is due to my Kadosh Nefesh; Hashem's honor takes effect on it. Through this, You raise my head above!
