Helloo, I've dealt with this vicariously through my neighbors and thought our experience might be of use to you:
Our house backs on to a field containing 2 horses. It's not secure against dogs or people but is against horses iyswim. There's a bloke across the road who had a Labrador and no garden, so regularly used the field without permission to exercise his dog. His dog never bothered the horses so the horse owner never said anything and would pick up the dog mess when she went poo picking for the horses.
About 6 months ago, LabMan got a second dog and obviously continued to use the field in the same way as before. One day I heard an incredibly loud and horrible scream from behind the house, looked out of the window to see his new dog (a jack russel type) with his teeth in one of the horses hind legs quite high up. Horse was screaming. Bloke was doing absolutely nothing.
Not entirely sure why, but I legged it outside, hefted myself over the fence and ran at the dog waving my arms and bellowing at the top of my voice and must have looked akin to a female New Zealand rugby player doing the Haka in my pink nightie and snowman slippers 
Dog clocked me and let go out of sheer astonishment I think more than anything and legged it back towards LabMan. Horse bolted down to the other end of the field but was obviously bleeding and in pain.
My adrenaline was through the roof at this point and LabMan had turned as if he was going to walk away so I literally RAN at the man and screamed "EXCUSE ME!!". He continued walking but at this point a couple of other neighbors and a dog walker had come out to see what was going on so I shouted "His dog just attacked the horses!" and one of the other neighbors shouted back that he was her next door neighbor, gave me his full name and told me which house he lived at.
Another neighbor had the horse owners number so I called her myself, told her what had happened and gave her the blokes details. She called the police and I was a witness and spoke to them, telling them what had happened. Police were round there within a couple of hours but the dog wasn't put down and nothing came of it. She did get him to pay for her insurance excess though!
LabMan hasn't been near the field since!
Have you thought about naming and shaming this bloke on social media? film him next time his dog does it and film his reaction, then post and ask if anyone knows who he is? Sometimes shaming people into doing the right thing is the only way they listen.
Angry for you OP 
Also, the taste for blood thing is indeed a myth, it will be the fun of chasing and biting that will be entertaining this dog not the blood :)