Here’s the Matryoshka Padlock v2: stronger all-steel construction, straddles one or both “legs” of the main padlock’s shackle for more locking room or more strength (not that it’s ever gonna let go of the key even with only one side locked 
) And unlike v1, it’s self-contained, so there’s no bits to lose:
Honestly at this point, if you want to steal the key, you’re better off sawing the key’s bow itself