Demarcate a 20-by-20-inch square at the desired fence post location, using stakes and string.
Dig out the area within the square 14 inches deep, using a shovel.
Compact the dirt at the bottom of the hole, using a hand tamper.
Fill the hole with 2 inches of gravel and sand. Compact the gravel and sand with the hand tamper.
Cut a square of wire mesh to fit in the hole, using wire cutters. Place the wire mesh squarely in the bottoms of the hole on top of small stones so it is elevated approximately 2 inches.
Mix water gradually to a dry concrete mix until you achieve a thick, soupy consistency. Mix concrete in a wheelbarrow or large bucket, using a shovel. Fill the hole with 6 inches of concrete. Level the concrete, using a concrete trowel. Allow the concrete to cure for the time indicated in the dry mix manufacturer's instructions.
Create a mortar mix. Combine six parts sand, one part cement and one part hydrated lime. Mix in water until you achieve a thick, goopy consistency. Add concrete pigment if you want to change the color of the mortar to better complement the stones. Allow the concrete to cure for 48 hours. Periodically mist the concrete with water throughout the curing process.
Lay the first layer of stones on top of the concrete footer. Add half of mortar to the concrete surface, using a trowel. Add 1/2 inch of mortar to the bottoms of stones and set them into mortar on the concrete.
Continue to build up the fence post to the desired height. The mortar between stones should be approximately 3/8 inch thick. If necessary, split stones to fit, using a chisel and a 3-pound hammer. Wipe any mortar that smears onto stones as it occurs with a damp sponge.
Cap the top of the post with one large, flat rock or with a concrete post cap.
Smooth down the mortar joints with a wood dowel. Hold the dowel at an angle and run the rounded edge along the mortar joints.
Paint the mortar joints with grout sealer, using a small, round paintbrush. Wipe any sealer that smears or drips onto stones as it occurs with a damp sponge. The stones can be painted with stone sealer. Sealers protect against water, mineral, oil and grease stains.
Cover the posts with plastic and allow the mortar to cure for 48 hours. Periodically mist the mortar with water throughout the curing process.