Dora Bas Rivka Silver O'H
How Sharper Than A Serpent's Tooth
David asks for relief from an evil pursuer (possibly Doeg, who informed on David and instigated the massacre at Nov) and from a person who seeks him harm (presumably Saul). They plot against him and are quite persistent in their attacks. They sharpen their tongues against David like a serpent's tooth.
David asks to be guided safely away from those who keep him on the run. They set traps for him, possibly referring to the people of Zif, who betrayed David. David called out to G-d, Who rescued him in his time of danger. (The commentators differ as to what the referent is.) David prays that the plans of the wicked not be permitted to succeed and the wicked themselves not increase in power and prestige.
David concludes by referring to a leader of his opposition, whom he prays will be undone by his own words. This appears to refer to Achitofel, a senior advisor of David's who deserted him and defected to join the rebellion of Avshalom. David prays for G-d's wrath to descend like fire from Heaven on such enemies, casting them into depths from which they will never arise (presumably Hell, but not necessarily). There's no place for slanderers in this world or the Next. David is confident that G-d will answer his plea, since He defends the oppressed. The righteous will praise G-d and enjoy His Presence.
The word "yadati" ("I know") in the penultimate verse is a kri/ksiv, in which the word is written and pronounced two different ways, leading to two different understandings of the text. Here, the word is spelled "yadata" ("You know"), meaning that G-d will take action because He knows the evil ways of David's pursuers first-hand.