I dealt with simply doing a basic repair like this last year. My problem is that the dam is so old I now have problems in other areas. The spot I had repacked holds fine. We used a big front loader and clay from my yard to do the repair.
I don't know how big your entire dam is, but I know when I get mine redone in about 5-10 years I am going to have the entire dam redone so everything is new and locked in together.
My pond is maybe a tad over an acre, was made in the 60s or 70s by blocking a ravine, and since it has some excellant fish in it I plan to keep it for now.
When the bad spot was repacked I also had the guy stick a lot of clay on the back of the dam to make it a more gentle slope so I could manage clearing it better.
