honestly, this isnt a bad idea. Making a man made moat (say that five times fast) would be cheaper than a wall, and cannot be easily destroyed. Also if it is used as a canal, it could become a means of transport like the panama
How so? If it is used as a commercial canal, it would pay for itself incredibly quickly. It wold have alternative uses, whereas a wall would be useless for everything except for its job. I highly doubt it's more expensive to break ground than add to it
Why would you say that? It's a great idea that would bring even more money simply because it exists. It cuts down the distancestors from places such as Japan to the east coast. It could be very useful