gadgetnut,
A different view....if money is not a major issue, then go with the excavation. Don't just get the cattails however, go to the clay removing all the muck and sediment that cattails love to live in. That should solve the problem long term so that any future uprisings could be handled by spot treatments. I'm not a pro on this topic, just a pond lover like you that does not use chemicals unless it's a last resort. I fear that the chemical approach, while it will work one season, will need to be re-applied again and again over time. If cost is an issue, chemicals may be your only choice, however.
Doing the excavation will, in addition, make your pond much more usable for all kinds of activities.
