Adam Clarke on Psalms 18:33

My feet like hinds' feet - Swiftness, or speed of foot, was a necessary qualification of an ancient hero. This was of great advantage in pursuing, combating, or escaping from a fallen foe. Ποδας ωκυς Αχιλλευς, "the swiftfooted Achilles," is frequently given by Homer as a most honorable qualification of his hero.

Upon my high places - In allusion to the hinds, antelopes, mountain goats, etc., which frequented such places, and in which they found both food and safety. God frequently preserved the life of David by means of these.