https://www.amazon.com/gp/product/B0084EGGR0/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Get one of these, it's what they use to train hounds to chase a lure.
The local LGRA club actually uses one sewn into a cheap coonskin hat as a race lure.
A few squawks and you will have his ATTENTION.
The loud squeaky is called a squawker or a predator call. At least that's what it is called on Amazon. Our girl hears it and will stop everything she's doing. https://www.amazon.com/Pete-Rickards-Scotch-Predator-Call/dp/B0084EGGR0/ref=sr_1_1?ie=UTF8&qid=1502748711&sr=8-1&keywords=squawker
https://www.amazon.com/gp/product/B0084EGGR0/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1
Get one of these. They're used for training, if a greyhound has raced, it's basically 100% they'll respond to it.
My local LGRA club uses them for race lures, sewn into a cheap coonskin hat from amazon. My hound is pretty laid back, but that lure gets his ATTENTION.
You could also try a rabbit call, they are used for greyhounds. My dog is part greyhound and if she takes off chasing something I am screwed (I can't let her offleash unless she's completely fenced in). I haven't bought one of these yet, but I plan too. You can practice with it and reward when your dog comes back.