A week without comment. Closing.

中辞典: 生き馬の目を抜くような sharp; shrewd
生き馬の目を抜くようなことをする use [resort to] sharp practices
東京は生き馬の目を抜くような所だから気をつけなさい. You must ┏keep your wits about you [be wide awake] in Tokyo, or you will be taken in by some ┏sharp practice [shrewd trick] or other.
ルミナス: 東京は*生き馬の目を抜くような所だ (⇒抜け目のないことが終始行われている) Shrewd practices are common in Tokyo. / (⇒情け容赦のない競争がある) There is cutthroat competition in Tokyo.
Tanaka: 彼は生き馬の目を抜くようなやつだ。He is a sharp-shooter.

I think this works. The sleeping weasel version was a bit, er, old-fashioned.

@@ -13 +13,3 @@
-<gloss>to catch a weasel asleep</gloss>
+<gloss>to be shrewd</gloss>
+<gloss>to be sharp</gloss>
+<gloss>to keep your wits about you</gloss>

daijs: 
生きている馬の目を抜き取るほど、すばやく物事をする。油断のならないさま。
prog examples:
生き馬の目を抜くような男
a shrewd man／《口》 a sharper
生き馬の目を抜くような大都会
a big city where sharp [cutthroat] practices are common

The Free Dictionary:
Catch a weasel asleep
To surprise someone who is normally alert, shrewd, or on-guard

ngrams
生き馬の目を抜く	11983

This entry was commented on here: https://mobile.twitter.com/practicaljp/status/1265403983817879553
I think the definitions could be improved, but I can't come up with anything better than "to be very fast at doing something"

@@ -13,2 +12,0 @@
-<misc>&sens;</misc>
-<misc>&obs;</misc>

@@ -16,0 +16,1 @@
+<gloss g_type="lit">to pluck out the eye of a live horse</gloss>