Cork screw eel grass is probably going to be your best bet. It will do fine in the deep south as it is not very cold tolerant. American pondweed should do well also. I think that combination would be a good option. Alligator weed is an emergent aquatic plant, while the other two are submerged aquatic plants, meaning they do not grow above the surface, for the most part. Options that would be suitable for an emergent to assist in keeping your pond banks from eroding and providing cover for fish would be species like sweet flag, pickerel weed, arrow arum, etc...