Adding the small section of magnetic material to the dropper, is a good idea, although rather tricky to mount, i'd imagine? You can wrap tiny offcuts of tissue paper (loo roll/kitchen roll) around the joints, then soak in superglue to reinforce. When dry, paint matt black to be less conspicuous. I preferred using Bachmann coupling hooks, being non-ferrous, they could never be magnetized. 

Hornby hooks are steel, so I always thought there could be the danger, of the Hornby hooks becoming magnetic, then the two hooks might stick together? Other people haven't reported this as a problem, so perhaps my concerns, have been proved wrong?

       It must be over ten years now, since I first described this uncoupling system, maybe it's time I 

wrote an updated account, in the light of experience? I'd have to do new photos too, the originals got lost, when photobucket withdrew their free hosting!

       I moved house nearly three years ago, all my railway equipment ended up in removal boxes. 

Nothing was lost, the removal firm were excellent, but even now I have trouble locating things. I'm building a new layout, which will incorporate the under-track magnets, permanent type in sidings, maybe electro-magnetic on running lines, to eliminate any mishaps, I could do a write-up as I progress?

       I used to use my own name on RMweb, but a few years back RMweb re-invented itself, I found it impossible to log back on, so I re-registered with the new name/avatar "Kirby Uncoupler"

                                                                  Cheers, 

                                                                        Brian Kirby. 

https://www.newcivilengineer.com/latest/ashamed-to-be-an-engineer-nce-readers-react-to-highways-england-bridge-infilling-15-07-2021/