Hello from Georgia,
I have heard of a method that seems to me to be near 100 % effective, yet have never had any personal experience with it. I have known a few professional coon hunters who have a method to break dogs from chasing deer, or anything else they do not want to be followed. They take the dogs afield and after setting up a trail of the undesired animal, they inject the dog with a substance that induces severe vomiting within a few minutes. Then, when on a good hot trail the dog will start to get sick while smelling the deer, or other undesirable critter and will relate that smell with the sickness. A few times of that and the dog will run from the smell that has made it sick. I am not sure what the injection consists of, but it is not serious and the dog recovers in a short time. This is pretty extreme, and some may say say unethical, yet from what I gather it is effective for the life of the dog.
Another method consists of crating the dog in a wire crate which is then hooked up to a 12 volt car coil. The crate is then covered and the undesirable critter( likely dead) is put under the cover as well and the coil cranked up to administer a series of shocks which the dog can not escape. The dog will connect the smell of the undesirable with the shock and find it is not willing to withstand the pain the next time it smells such a critter.
Yet another method is similiar to the 55 gallon drum mentioned above. I know a man who had a dog that would not stop killing chickens. He took a few of the dead birds, put them in a burlap sack along with the dog and then beat the sack with a few of the other dead chickens. As soon as the dog was loosed from the sack, he no longer had ANY interest in even going near a chicken. A bit extreme, yet effective.
I am niether condoning nor condeming the methods mentioned here. I have never been personaly involved in them, but as a witness to some high performance and well trained dogs, they no doubt work. There are assuredly other methods that may be less traumatic to a dog, but hey, if they work, and the dog suffers no lasting harm, how can one say that it is wrong ?
Just some thoughts from an old time hardcore dog man who above all else is a working dog lover.God Bless You All !!
Dave