The grammar in this psalm just slays me. Lots to fiddle with, lots to squint at cross-eyed to try to make it work. There’s violence ahead; please don’t blame me.
With psalms like this one, which makes no explicit connection to an event in the life of David, I try to imagine when and where in his life it would make sense for it to be composed. In broadest terms, David is opposed by the multitude and crying for God’s deliverance in the early half of his story (I Samuel 18-31) and so we should tie it to something in there. I’ll say it’s thematically linked to the wilderness years and being betrayed by the Ziphites to Saul.
“Nonne Deo” (Psalm 61)
 In finem, pro Idithun. Psalmus David.
Unto the end, for Idithun. A psalm of David.
 Nonne Deo subjecta erit anima mea? ab ipso enim salutare meum.
To God it will be subject, my soul, will it not? for from Him my salvation.
 Nam et ipse Deus meus et salutaris meus; susceptor meus, non movebor amplius.
For He both my God and my salvation, my upholder; I will be moved no further.
 Quousque irruitis in hominem? interficitis universi vos, tamquam parieti inclinato et maceriae depulsae?
How long do you rush upon man? everyone of you slaying us, like to a leaning wall and a toppled fence?
 Verumtamen pretium meum cogitaverunt repellere; cucurri in siti; ore suo benedicebant, et corde suo maledicebant.
But truly my price they have thought to drive back; I have run in thirst; with their mouths they were blessing and with their hearts cursing.
 Verumtamen Deo subjecta esto, anima mea, quoniam ab ipso patientia mea;
But truly to God be it subject, my soul, for from Him my patience.
 quia ipse Deus meus et salvator meus, adjutor meus, non emigrabo.
Since He is my God and my Savior, my Helper; I will not depart out.
 In Deo salutare meum et gloria mea; Deus auxilii mei, et spes mea in Deo est.
In God my salvation and my glory; God of my aid and my hope is in God.
 Sperate in eo, omnis congregatio populi; effundite coram illo corda vestra; Deus adjutor noster in aeternum.
Hope in Him, the whole congregation of the people; pour out before Him your hearts; God our helper unto the eternal.
 Verumtamen vani filii hominum, mendaces filii hominum in stateris, ut decipiant ipsi de vanitate in idipsum.
But truly vain the sons of men, lying the sons of men in the scales, that they may deceive, these same, from vanity in the self-same.
 Nolite sperare in iniquitate, et rapinas nolite concupiscere; divitiae si affluant, nolite cor apponere.
Hope not in injustice and rapines desire not; riches if they flow toward, place not the heart.
 Semel locutus est Deus; duo haec audivi : quia potestas Dei est,
Once has He spoken, has God; these two have I heard: that power is of God
 et tibi, Domine, misericordia : quia tu reddes unicuique juxta opera sua.
and to You, O Lord, is mercy; that You repay to whomsoever according to his works.
v. 2 Nonne sometimes causes problems for my style of translation. By itself it’s no big deal. It seeks the approval or agreement of the listener through a negative, as in the English “Beautiful day, isn’t it?” The problem (for me) is that Latin can separate nonne from the main verb, but English needs to keep them together. Throw in the word order of this particular line and things just get ridiculous trying to preserve word order in moving to the English. It pains me to do it, but I can’t see a clever way to make this line work without breaking at least one of my rules.
v. 4 tamquam…depulsae. Sigh. There’s not reasonable way to take this Latin without doing something weird. The Septuagint has a dative construction here as well, which is slightly less weird since dative shows location in Greek. That’s still a weird way to do it but not gibberish at least. But the dative in Latin doesn’t work that way and interficio doesn’t take a dative object. The only remaining move I can see is to take tamquam as an alternative to similis, which does take a dative. Believe me, I’m not happy about it.
v. 12 duo haec. What follows is a bit odd, but quia should be taken as introducing each of the two things. The first thing has two items joined as one: that both power and mercy are God’s. The line break obscures this a little I think, making it seem like power and mercy are the two things. The merciful God is powerful, and He is the Judge of repayment for deeds. Both dreadful and hopeful.