moat, ditch, canal, Australia
濠 centers on a water-filled excavation: a moat, ditch, or canal. The Australia meaning is a modern phonetic usage unrelated to the core idea.
濠 combines 氵 (water) with 豪, which likely contributes the sound and the idea of a large or impressive structure, suggesting a grand water-filled trench.
Water 氵 beside a grand, impressive structure 豪: imagine a magnificent castle surrounded by a wide, water-filled moat.
For ゴウ, picture a grand moat around a castle, and think of the word 'go' as in 'go around' the castle: go -> ゴウ, and the water-filled ditch encircles it.