Augustine of Hippo

What then followeth? "The loftiest hills are for the stags" (ver. 18). The stags are mighty, spiritual, passing in their course over all the thorny places of the thickets and woods. "He maketh my feet like harts' feet, and setteth me up on high." Let them hold to the lofty hills, the lofty commandments of God; let them think on sublime subjects, let them hold those which stand forth most in the Scriptures, let them be justified in the highest: for those loftiest hills are for the stags. What of the humble beasts? what of the hare? …

On the Psalms, Psalm 104 ↗

Jerome

The high mountains for the stags. This animal kills serpents and eats them. Therefore it fittingly dwells in the mountains, this one that slays the intelligible serpent — the one who was wiser in paradise than all the beasts, who deceived Eve. The rock is a refuge for the hedgehogs. He who is timid has the rock as his refuge: and the rock is Christ.

Homily 30, on Psalm 103 ↗

John Cassian

And so by the illumination of God himself he mounts to that manifold knowledge of him and begins to be nourished on more sublime and still more sacred mysteries, in accordance with these words of the prophet: "The high hills are a refuge for the stags, the rocks for the hedgehogs," which is fairly applied in the sense we have given, because whoever continues in simplicity and innocence is not harmful or offensive to any one, but being content with his own simple condition endeavors simply to defend himself from being harmed by his …

Conference 10:11