I'm in a similar situation and have been looking at doing some form of Seawall or Sheet piling for the 75ft directly in front of our house where we mow. However, most sheet piling options are really big and not suitable for small scale ponds or residential use.

The product I feel will work the best for my application is found in the UK and I have been unable to find a source in the US. It's a scaled down solution that could be installed with a mallet or deadblow hammer given our soft soiltype.

Multilok Sheet Piling

Another option I play with is using 4" PVC pipe cut into 18-24" lengths and pounded into the soft clay. I can insert wood down into every 4th or 5th tube and then cap with a composite 2x6 to give the bank a nice finished edge. The pipe will be flush with the high level mark so the tubing itself should not be visible once it's all done.