Longer Retaining Walls

I like to have longer retaining walls so when i fill up the see it is more orderly. Imagine having a port area where it is completely straight. It would look so much better and it would save up some dumping materials too.

Retaining walls that can go in the ocean would be interesting but probably hard to implement and/or use, given how uneven and deep the sea floor can be. Really, I think what you'd want would be the ability to dump directly onto the sea floor rather than having to let it spill in from the shore, yes? So you could say "I want to fill in everything up to -5" or whatever like you can on land. Having an even bottom would then make it easy to put down walls and fill in land on the other side, assuming we were allowed to put walls in the water. In the other direction, there is the possibility of dredging the sea floor without getting rid of the ocean above it first, which would probably make the people happy who are obsessed with that one bit of sand on Dragontail Island or whatever.
As for me, it's an interesting idea but not one I am going to advocate for as a priority over other things. Sorry. But I hope you found my thoughts useful!