Thanks very much for all the replies. My plans were to make a driver similar to what I've used 1000's of times to drive T posts on our farm, except with a long handle on it. I am going to make it light enough to keep from getting too fatigued, but heavy enough that it won't take but one or two licks to drive the slats. Good idea about it needing to float. I might just tie a rope with a float to it. I can design it so that it will have little bouyancy and also where there will be little water resistance when driving the stakes.