I will hold good thoughts for your duck.
We had a similar experience, except with wedge-tails. Our cat saw them off!
Insane cat!
While I like MOST dogs, Pomeranians, Shi-tzus, Maltese Terriers etc. are natively quite vicious dogs - its a good thing they aren't the size of Rotweillers - and I find them objectionable. More people are seriouslly bitten and pets mauled by these aggresive little fur-balls than all the pit-bulls, dobermans and rottweilers combined (RSPCA figures 2007).
I hope you get satisfaction from the owners / council, but apart from that good solid fencing and perhaps a dog of your own are really the only defence. A sound Staffy ***** makes an excellent guard dog; good with kids, easy to train to keep away from other pets, and pretty uncompromising of invading canines. I mean you
could shoot the offenders, but you don't strike me as a dog-killer.
Good luck and you can always borrow my Jack Russel if push comes to shove. He IS nuts!