[tetraca]

> where I will probably embarrass myself by suggesting 犭(dog) + 瓜 (melon) = 狐 (fox), which, though cute, feels like as much a false etymology

I don't know Japanese but with what I know about classical Chinese character construction, I'd expect that melon acts as a phonetic hint and dog hints at the meaning (e.g. the word this character represents sounds like "Melon" but is related to "Dog").

Edit: I was curious and looked it up, it's exactly this https://en.wiktionary.org/wiki/%E7%8B%90#Chinese