talk about the fox in the henhouse

fox in the henhouse means, idiomatically or figuratively, a predator loose among the prey, a person likely to exploit the information or resources that he or she has been charged to protect or control. E.g.
My sister is going to put her ex-convict brother-in-law in charge of her business, and I'm worried he'll be like a fox guarding/in the henhouse.

Η φράση «βάζω τον λύκο να φυλάει τα πρόβατα» σημαίνει ακριβώς αυτό το πράγμα.

(Θα μπορούσα να προσθέσω ότι δεν έχει σχέση με το «wolf in sheep's clothing».)

Many thanks, Duke. Is there an idiom which corresponds with 'talk about'? Would μιλάμε για... serve the purpose?

Χμ, ναι, βιαζόμουν λίγο και έκανα μισή δουλειά. Για να δούμε:

My sister is going to put her ex-convict brother-in-law in charge of her business, and I'm worried he'll be like a fox guarding/in the henhouse.
Η αδελφή μου σκοπεύει να βάλει υπεύθυνο στην επιχείρησή της τον κουνιάδο της που ήταν κατάδικος, και ανησυχώ ότι βάζει τον λύκο να φυλάει τα πρόβατα.

Για το «talk about» υπάρχουν καναδυό επιλογές, ανάλογα με την περίπτωση. Για παράδειγμα:

* Talk about a stupid thing to do! I can't believe you did that! – Μιλάμε για μεγάλη ανοησία! Δεν το πιστεύω ότι έκανες τέτοιο πράγμα! (από εδώ)
* I've just spent six hours babysitting my cousin. Talk about boring! – Μόλις πέρασα έξι ώρες προσέχοντας το ξαδελφάκι μου. Αυτό θα πει βαρεμάρα!
* Have you seen John's new car? Talk about a pile of junk... – Είδες το καινούργιο αμάξι του Γιάννη; Αυτό κι αν είναι σαράβαλο...

Για τη φράση του τίτλου, πάντως, μπορεί και να μην το χρειαστείς. Αν κάποιος αναφέρει κάτι και μετά το σχολιάσει με «Talk about the fox in the henhouse!», αυτό μπορεί να μεταφραστεί απλώς «Έβαλε/βάζει τον λύκο να φυλάει τα πρόβατα!»

Talk about a comprehensive reply! Since on this occasion I feel somewhat humbled, just for once I shall playfully address you as 'Your Grace' ( η εξοχότητά σοας) the correct mode of address from a social inferior to a duke...:lol:

κοίτα να δεις!

...
In the same vein, but including the fox: Βάλε το λύκο μπιστικό, την αλεπού δραγάτη.

The quick brown fox jumps over the lazy wolf. A flash in the pangram.

Thanks, Duke, for your help & your gracious invitation but on that occasion I will be entertaining Her Majesty in my humble cottage, being one of Her closest advisers but my thanks for Your Grace's kind invitation. I will mention to HM the dilapidated state of your ancestral seat. She is sure to help.
Earion, you need no title for your name is as mysterious as it is obscure but your knowledge is excellent & your help to me highly valued....:):)

Mysterious? Obscure? Not at all. It means "The Mariner" in (J.R.R. Tolkien's) Elvish; and it's all loquaciously but clearly explained here.

And apparently Tolkien took the root of the word from Cynewulf because the sound was pleasing to him. There Cynewulf uses it to refer to John the Baptist, the morning star, as the herald to Christ, the rising sun:-
éala éarendel engla beorhtast / ofer middangeard monnum sended
"Hail Earendel, brightest of angels, over Middle-earth to men sent".

In your 'loquacious but clear explanation', Earion, is κόλπο the subject of this phrase in brackets:

Θαμπώναμε τα κορίτσια με τις διηγήσεις μας (πόσες φορές δεν έπιασε το κόλπο), το παίζαμε κάτοχοι ενός ακριβού μυστικού, οι ονειροπαρμένοι, οι πέρα απ’ τον κόσμο τούτο.

The meaning therefore seems to be 'how many times did the trick not succeed' i.e. 'The trick always worked' :)

Precisely.