As for the head of those that compass me about - Luther renders this, “The calamity which my enemies design against me must fall upon their own heads.” The passage stands in contrast with Psalms 140:7 : “Thou hast covered my head,” etc. As for his own head, it had been protected in the day of battle. In reference now to the heads of his enemies - of those that compassed him about - he prays that what they had designed for “his” head might come by a just retribution on their own. The phrase “compass me about” refers to his enemies as being numerous, and as surrounding him on every side. See Psalms 40:12; Psalms 88:17; Psalms 109:3; Psalms 118:10-12.
Let the mischief of their own lips cover them - Come upon them. The mischief which they have designed against me; that which they have conspired to bring on me. The reference is to a combination against him, or to some agreement which they had made to destroy him.