After finishing a game with Dunga, we both felt the attacking was one-dimensional. So I added submarines (and their infrastructure) and more connectivity in the middle. Each submarine costs -5 income if taken, and each country's sphere of influence has 5 submarines visible (they connect to ships in their squares), at least 1 for each enemy. So the threat of a submarine attack is present. But only the attacker will be likely to take the submarine to preempt the threat: 9 territories in the submarine infrastructure are worth +5, and they lead to all 5 of one's submarines; but since it costs one -5 to engage in submarine warfare, the aggressor is likely only going to attack 1 submarine, since the bonus only offsets 1. The Japanese game of go has a name for a similar strategy, something like bitter pill (I don't know what it's translation is): a stone that is not taken and ends up causing great harm deep in one's core area. I'm hoping the submarines will function this way.
http://WarLight.net/SinglePlayer.aspx?PreviewMap=14978