Snide, consider spraying the cattails with glyphosate (sold as Roundup and under many other names and at a wide range of prices) you can get at any feed store or farm supply. Using label instructions for mixing, spray the cattails from the bank and, if necessary, from the pond side as well. Wait a month or two and re-apply as necessary to remaining plants. Steepening the bank would be a move that I think you would regret later when you mow the grass on the bank.
