1)
Why does it say "Magini Al Elokim"?
1.
Radak: It should say Magini Elokim! Rather, this teaches that my trust and reliance is on Elokim, that He will be my shield.
2.
Malbim: Because Hashem tests hearts and kidneys, He will be my shield. He saves those of straight hearts - "Heitivah Hashem la'Tovim veli'Ysharim b'Libosam" (125:4).