"Mike, if you're going to use solid wood make sure that you glue them down or you run the high risk of splitting and breaking. Plywood doesn't have the splitting and breaking problems but will be a lot more durable than the solid wood, but…"
"It will hold until water gets in! I have seen lots of rotted plywood rub strips. Solid wood doesn't have the same issues. It will still rot obviously but has a greater ability to keep water out as there isn't all the potential entry points…"
"David, I know they promote rot. Here's pictures of a Sawyer oar I bought and a picture of the repaired oar. I cut it back to good wood and scarfed a new piece of Douglas Fir and Ash. I keep a good coat of finish on them and they work well.…"