OCD, many homeowners are getting sheets of plastic interlocking sheet piling. They don't have the nice locking feature or the expanded areas for posts to go in, but they are lightweight and easy to install. Simply get a 2-3' section of 1" PVC and adapt from PVC to garden hose thread. Then put a good supply of water down the 3' pvc at the base of the sheet piling. With water flow and a little pressure or tapping with hand tools the sheet will slip into place. You have several options for capping the top.
Folks I know did about 100 feet in no time at all with 2 guys and no special tools except hammers and garden hose. I'm sure there is an art to getting it to follow a straight line or follow a special curve without looking like a do-it-yourself special when you are done but that separates the pros from the DIY crowd.
We (Dad, a friend and I) did just that back in the late 1970's with I believe 5/16" thick Cor-10 steel "W" piling sheets. They came in IIRC 22' sections, we cut them with an abrasive wheel on a circular saw and washed/pounded them in. We did a 75' seawall in 2 weekends.
