Charles H. Spurgeon on Psalms 108:9

Over Edom will I cast my shoe. David overthrew their army in the "Valley of Salt", and his general, Joab, following up the victory, destroyed nearly the whole male population (1Ki 11:15-16), and placed Jewish garrisons in all the strongholds of Edom (2Sa 8:13-14). In honour of that victory the Psalmist warrior may have penned the words in Ps 60:8, "Over Edom will I cast my shoe." —J.L. Porter in, "Smith's Dictionary of the Bible."