If the yard is big enough and he is happy enough, you should only need the bottom to go to the ground, and the fence should be about 6' high. Medjai does great with 5' wood fences that go just to the ground, he doesn't climb or jump up unless there's a squirrel, and that's just to see the squirrel, then he's fine without attempting to get out, and he can even fit through the gate, so we worry all the time.
I don't know if you were considering an electric fence. That may be an option, or at least worth trying if you really want the view. I'm not sure what it's like all around you, but I don't think you should have an issue with the water, that should be good enough to keep roo out of the river.