Personally, I really dislike keels on canoes. When I ordered my Old Town Guide in 1972 I specifically custom ordered it without a keel. None of the canoes I ever bought or built had keels and whenever possible the canoes I sold as a dealer for most of the major brands were keelless. Part of learning to become a really good paddler has to do with being able to move your canoe in directions other than just forward in a straight line, including purposely going sideways. A keel then may become more of a hindrance than a helper. Native Americans and Voyageurs did pretty well without ever having keels on their canoes. The canoe keel was a later, white man's invention, and not likely his best one. Perhaps it was to offer a bit of damage control, perhaps as an attempt to make up for lack of paddling skill. As for rock damage - hit a rock and it will likely damage something to some degree, and keels neither prevent that entirely, nor are immune to damage themselves.