Dig a hole that is 3 feet deep, using a post hole digger. Make the hole at least 1 foot across.
Add 4 inches of gravel to the bottom of the hole. Pack the gravel down with a tamp. Set the metal post on the gravel in the hole. Adjust the post so it is centered in the hole and level. Use a torpedo level for vertical adjustments.
Add 6 inches of gravel around the post. Pack the gravel down firmly with a tamp to brace the post in place. Check the level once again with the torpedo level.
Pour quick-set concrete into the hole. Fill the hole to within 6 inches of ground level. Add water to the quick-set concrete. Refer to the concrete manufacturer's directions for the exact amount of water to add.
Fill in the last 6 inches of the hole with dirt after the concrete has hardened and cured for 24 hours.