I don't know that any advice I can give you will help, because our locations and soils might make local practice of "what works" different.
+1
But here's something that really worked for me. Nothing seemed to grow on the dam, which was constructed from high clay subsoil-little to no organic material, basically no topsoil. I didn't have the soil tested, but most clayrich soils at least in my area are very acidic, and contain very little calcium. I limed the dam very heavily with pelletized lime-presto, really amazing difference. 5 years later, the small area at the tail of the pond that I didn't bother liming STILL has minimal growth, the rest of the dam is very thick lushly carpeted.
Again, this might not apply to your situation at all, but it's something to consider--and really cheap to buy pelletized lime. I just spread mine with a garden spreader, and threw it on the steeper areas by hand.
