I like the idea of shaping the ditch to be easily mowed. That is doing it the "right" way the first time.
I also like the ring of rocks (maybe with some underwater screens?) as a first layer of protection to keep leaves and fish off of your screen on the culvert.
Does anyone fish your pond? If so, you could place one large, flat rock in your ring of rocks. I think that would look attractive AND be a magnet spot for kids to cast from while fishing in your pond.
