As someone who's caught a leaker in the past (well, someone that was exfiltrating company secrets to a competitor) catching leakers is actually pretty easy if you have any modicum of control over the tools they use and the places they work. Barring that, no. Just no. It's not going to happen.
If a leaker is gullible and stupid some trickery is possible but I wouldn't get my hopes up, Warner Music. Seems like a job that's doomed to fail from the start. I wouldn't even bother unless they know it's just a job on paper and are actually just looking to give someone's kid a legit-sounding job to pad their resume 🤷
Not only that but if I were in charge of hiring I'd be extremely skeptical of any and all applicants. Anyone smart enough to do the job will know it's impossible and will just become a master of stalling and picking low hanging fruit (aka useless) and everyone else is just a fraud.
This reminds me of the scene in Better Call Saul where Mike interviews contractors for their construction project. He rejects everyone that says they can do it and hires the guy that tells him it’s impossible.
These leaks frustrate labels and artists and not just for financial reasons. Many musicians work months if not years on their tracks; seeing these being paraded on pirate sites, before their official release, stings.
I dunno about this. Most of the artists I give a shit about have their music up for free on Bandcamp. The ones I've asked point-blank about it have said that they don't care about piracy; they see it as free advertisement for their live shows, which is where they make most of their money (and on merch sales). This might be true of some of the largest acts, where sales might make up more than a few hundred dollars in total annual revenue, but probably a lot less true for most mid-sized or smaller acts.
OTOH, given that the labels are the ones making money off sales of music, they probably care quite a lot.
It's the same as content creators say you shouldn't use adblock because it defrauds youtube. They don't care about youtube. They only care about their own money without saying they only care about their own money.