Chapter 241: The War that Decides the Fate of 'The Bridge' Part 44
Making a moat isn't really that big of a challenge. All they have to do is make a huge hole that can't be easily trespassed by anyone, including a huge army, and then fill it entirely with water so that it will prevent anyone from passing through easily.
Honestly, after seeing the siege machines the Assembly of Freedom has prepared for this war, making a moat and trenches is probably the best idea as it would prevent those close-range siege machines from approaching the Dream Village.
Now, as long as they construct the moat wide enough that it would make the Dream Village outside of the range of the siege machines, then they won't have to worry about it anymore. Albeit that would be impossible. Nevertheless, they could still minimize and make it troubling for them to hit a target.
However, before that, they have to do something else first.