Regarding the method of marking the tone, I personally feel that the "children's rhyme of the standard method of tone" taught by the elementary school teacher is very effective, and this is how I have been used all my life.
The nursery rhyme that my elementary school teacher taught me back then was like this: don't let go of A's mother, don't find o, e, i, you are juxtaposed at the end;J, Q, X are naughty, and they dig up when they see you.
When you grow up, especially at this moment, answer your question for thoughtful consideration, or attach some theoretical basis: Mandarin has 39 finals, including 23 single finals, 23 compound finals, and 16 nasal finals. The tonal annotation of Hanyu Pinyin is marked on these finals, and the law is that the compound finals and nasal finals are marked in the order of a o e i u ü, and when ü meets j q x y, two points should be removed;When i and u are juxtaposed, whoever is behind is marked on whose head. The single rhyme is self-sacrificing.
Now, let's look at your specific problem, is it easy to solve: the finals of the syllable hou are ou, and its tone has four tones: yin ping, yang ping, upper sound, and de-sounding, the syllable has no soft sound, and it belongs to the compound vowel, which is applied to "no a to find o, e", and it can be marked on the "o" head.