Given these two factors, some player actions are real clear. 1. You need to isolate yourself from the opponents, by wall or dock block. 2. You need to build at least one dock.
So since you are building the dock anyway, why aren't you blocking the shallows with it? Even just putting it there when it doesn't fully block allows you to wall less, and gives the impression to your opponent that it is blocked.
Also, if you have the choice of either end, build it on the opponent's shore. It gives you a chance to wall your end later while they are destroying your dock.
Some people say that they don't like dock blocking because it doesn't maximize fishing. My answer to them is, "Build more than 1 dock. Move the boats later." Fishing boats seem to do ok with the pathing routes.