Yeah, I was assuming it was onomatopoeia for 2 reasons - it’s a doubled sound, it’s described as an adverb taking the と particle in Jisho. I maybe wrong, the above was my guess at trying to breakdown the end of a sentence where I didn’t really understand how it worked.
I did find this in an article on onomatopoeia usage. This would support I might be on the right lines if どうどう here is acting like onomatopoeia:
Summary
The ADJECTIVE usage (describing an object/condition) is actually a specialized application of an adverb. Grammatically speaking, the onomatopoeia wants to be an adverb, so we need to do some linguistic acrobatics to make it modify a noun.
How do we turn an adverb into an adjective? We “format” it with either とした or している. Don’t concern yourself with the meaning of とした／している here because there really isn’t one, we’re just using the formless verb する as an intermediary between our onomatopoeia and our noun.
とした is kind of the “correct” way to make an adjective usage, and している (usually abbreviated to してる) is the “casual” way, but they’re both doing the same thing: taking a sound and “formatting” it so that it can modify a noun.
Onomatopoeia are not defined by doubled sounds or by taking と. From the same article (堂々 is mentioned in the last paragraph):
Pseudo-Onomatopoeia
Pseudo-Onomatopoeia
One of the things that complicates the issue of learning onomatopoeia is that in addition to words like ちょっと and ゆっくり, which are so common that we don’t really think of them as onomatopoeia, there are also words that sound like and which may even be used like onomatopoeia, but aren’t.
You probably know a couple of these already too: いろいろ is an example. For all intents and purposes, you could consider this word an onomatopoeia, but its meaning is derived from the kanji (色々) rather than the “sound” of the word. Other examples of this kind of pseudo-onomatopoeia are 段々（だんだん） and 次々（つぎつぎ）.
Since these words aren’t really onomatopoeia, you have to be much more careful about which particle you select (if any). The above-mentioned three can all optionally take と, but others such as まだまだ（未だ未だ）, 別々（べつべつ）, and 元々（もともと） can never take と. Still others such as 堂々（どうどう）、延々（えんえん）、and 朗々（ろうろう） will always appear with と. Don’t worry about remembering all the specifics, just understand that not all words which sound like an onomatopoeia are.
「オオカミの偉大な王よ、僕は君の知恵、誇りの高さ、妻を大切にする姿を忘れない。」
“Great Wolf King, I will not forget your wisdom, your great pride, the way you cherished your wife.”
そして、悲しくなりました。
And it made him sad.
ロボたちオオカミは、どうして家畜を襲うようになったのでしょう。
How did Lobo’s wolves reach the point to attack domestic animals?
それは、人間がオオカミたちの棲家だった自然を壊し、ロボたち獲物の動物が、どんどん減っていったからです。
That is because humans have destroyed the wolves’ natural habitat, and the prey animals for Lobo’s wolves have been steadily decreasing in number.
オオカミがすべて悪いとは、言えないのです。
You cannot say that wolves are all bad.
To me sly is not inherently negative or bad. It has more of a secretive nuance than a deceitful one. “doing something on the sly” can be somewhat negative as one is doing something in secret (not being upfront about something), possibly lying a bit (or lying by omission). In some cases it can even be taken as a charming trait (“Han Solo, you sly dog you”). To me it’s not the same as clever really at all, but is certainly not devious, which is the most negative of the lot. This is my perception though and based on my experiences and opinions.
Seems like most dictionaries disagree with me though and label it as cunning and deceitful with a markedly negative undertone. I guess I just don’t use it that way. I use it more as like just cunning and secretive. If I want to be negative I’ll use more common words for that in my own expression. I don’t think sly is as commonly used these days though to describe anything other than a fox… so it’s usage is pretty limited for most people. (edit: I am specifically meaning when talking, not in writing where it is more commonly used)
そのことをたくさんの人に知って欲しいと思いました。
He [thought that he] wanted to make that known to many people.
そして、シートンは、ロボのことを『カランポーの王者ロボ（オオカミ王ロボ）』という物語として、発表しました。
And then Seton published Lobo’s story as a tale called “Lobo the King of Currumpaw (Wolf King Lobo)”.
この作品は、評判になりました。
This work became popular.
それから、シートンは、動物の物語をたくさん書きました。
After that, Seton wrote a lot of animal stories.
日本では、『シートン動物記』の名前て、親しまれています。
In Japan, they are popularly known as “Seton Animal Chronicles”.
これらの物語は、たくさんの人の心を動かしました。
These stories touched the heart of many people.
「野生動物を守ろう」という考えが、世界中に広がったのです。
“Let’s protect wild animals” - the thought was spread all around the world.
そして今も、動物や自然を愛する人々を育てているのです。
And also today, it raises people who love animals and nature.
アーネスト・トンプソン・しーとん（一八六〇〜一九四六年）
Ernest Thompson Seton (1860-1946)
自分で図鑑を作った
He made his own field guide
シートンは、こどものころ、こつこつとお金を貯めて、『カナダの鳥類』という図鑑を買いました。
As a child, Seton steadily saved up money and bought a field guide called “Birds of Canada”.
図鑑を見ながら鳥を観察するうちに、いくつも間違いがあることがわかりました。
As he observed birds while looking at the field guide, it became clear that there were many mistakes.
そこでシートンは、その間違いを赤いインクで直していきました。
So Seton corrected these mistakes with red ink.
しまいには、その書き込みで、図鑑は真っ赤になってしまいました。
At the end, with those additions, the field guide ended up bright red.
From the same article (堂々 is mentioned in the last paragraph):