Translation:This watch is sturdy.
Interestingly, the kanji for "sturdy, durable" 丈夫な (joubu-na) is the same for the Chinese character for "husband" 丈夫 (zhàngfū).
The Japanese kanji for "sturdy" is made up of the characters 丈 "measure" and 夫 "husband, man". So perhaps this gives some insight into the traditional culture and values of Japan! (or perhaps not, I'm just guessing)
If "好" is the exception, then there are so many exceptions to your rule:
妻 – wife / 嫁 – bride / 婿 – bridegroom / 姉 – elder sister / 妹 – younger sister / 娘 – daughter / 嬢 – Miss; milady / 姫 – princess / 妃 – queen / 妊 – to become pregnant / 婚 – marriage /
妙 – strange; mysterious / 嬉 – happiness; joy / 安 – peace; calm / 姿 – figure; appearance / 要 – necessity / 数 – number / 桜 – cherry blossom / 努 – to endeavor; to make an effort / 委 – to entrust / 接 – to join / 始 – to begin /
Definitions from Kotobank.
Joubu (https://kotobank.jp/word/%E4%B8%88%E5%A4%AB-533120) (1) gifted with good health; healthy (2) a thing that is well-made and hard to break (3) certain; definite
Ganjou (https://kotobank.jp/word/%E9%A0%91%E4%B8%88-470179) (1) healthy (joubu) body; also durably-made things (2) a horse's excellent health; also the horse
So it seems that "ganjou" has the meaning (1) and (2) from "joubu", so it can be a synonym in those situations.
sturdy = doesn't break easily
"This wristwatch is sturdy" => "This wristwatch won't break"
A watch is a wristwatch or pocket watch, basically a watch that you can carry around, while clock would always reffer to a big stationary clock like an alarm clock that always stays near your bed or a grandfather clock (the one that has a bell-like thing inside and rings like every hour). Im not a native english speaker myself but im confident in my knowledge (just keep in mind there might be an exeption i can't think of right now)