Tom,
Since Cattails propogate from Rhizomes, as long as the Rhizomes are intact and healthy and the depth of water is about 3ft. or less they will normally come back. The head of the cattails, when exploded and blown by the wind will lead to pollination.
Cutting the heads prevent pollination and will slow propogation. You are limited by your ability to not only eliminate your cattail heads but also those within many miles arounds that are carried by the winds from other ponds and lakes.
Cattails are very invasive, like bamboo. The best way to eliminate them is to dig them out (Rhizomes and all). I did this when I dug out my pond that had silted in. I used the silt/mud to fill in a small ravine on my property. There was not enough moisture to support the rhizomes so they died and added to the organic matter in the soil.
You mention changing the slope of the bank. That really does not have any bearing since the cattails will grow in soil that is moist to about 3ft of water depth.
Use herbacide if you must, but please as an absolute last resort.
Good luck,
J.W.
