Determine where you want to build the seawall along the edge of the water. Place stakes in the ground where the seawall will be located. Tie a string onto each stake to indicate the position of the seawall.
Dig a hole for the metal posts with the post hole digger to a depth of 24 to 36 inches. Repeat this step to dig a hole every 5 to 6 feet along the length of the wall.
Insert a metal post with threaded studs into each hole. Mix concrete in wheelbarrow by following the instructions on the package. Fill the hole with the concrete using a shovel. Allow 24 to 48 hours for the concrete to dry.
Place a level on top of each post to ensure that each post is sitting level to the ground.
Measure each 2-by-12 board and make a mark where the mounting holes need to be located using the pencil. Drill mounting holes into the wood with the power drill.
Place the 2-by-12 boards over the threaded studs on the metal posts. Place a washer over the threaded stud and then hand tighten a nut. Tighten the nut on the stud with the socket wrench. Repeat this step to install the remaining wood boards for the seawall.
Place a layer of rocks or gravel at the bottom front of the wall to prevent erosion. Add gravel or rock as a back fill behind the seawall and then add topsoil.