You do not need a shock collar or a prong collar. You need to teach the dog the "leave it" command. I will give you a short idea of how a lot ( yes I know there are lots of other methods) of animal trainers teach this to dogs and owners. I have had a German Shepard who would leave a cat that he was in mid chase in our yard. I have in the past had terriers, German Shorthair, and mutts, all of who learned this command. I at this time have a poodle and a male bulldog. None of my dogs would go after something I or my husband told to "leave it".
Start this training in the house. Then after the dog is good at it in the house move outdoors.
1. Get some very small training treats. I use Bil.jacs Little. Jacs. You can also use dried bits of meat or bits of cheese or hot dogs.
2. Sit on the floor, put a small treat in your palm, with your hand closed, let the dog sniff it. Then put your hand on the floor, rest it there with the treat enclosed. The dog will be sniffing the treat and your hand. Don't let him lick or eat the treat though. Tell him several times LEAVE IT. In a calm yet serious voice. At the instant the dog figures out he isnt getting the treat he will start to loose interest. At the instant the dog shows a lack of interest-- this could be different with different dogs, I have had some that shake their body, some that sit down , some that look at me trying to figure out what I want, give the treat o the dog with what ever command you use to show its ok. For me that is the word OK. That means go ahead for several things, like eating a treat, going through a door or out the gate. Praise the dog and pet him.
3. repeat step 2 a few times.
Do this several days or on till your dog gets it. Your dog wants to make you happy and he wants a leader. So if he can not learn this look at what you are doing.
I know people often think formal training takes a lot of effort and time, but your dog doesnt have the attention span you do so short and often is all you need to do. I give treats only after a command, and I give treats everyday. So through out my dogs life I "train" everyday. Every time we go outside when they wait to be released to go out the door, every time when they are able to go out the gate. Every time we go for a walk.
Ok now you move on to the next step. Put the treat in your hand then ( watch the dog carefully!) put the treat on the floor.....be ready....the dog will go for it, loud ( not a shout) stern, I mean business voice...LEAVE IT! Be ready to slap your hand on the treat, or step on the treat. Uncover again and repeat. after the dog leaves it give him a treat from your hand , not the one on the floor. When he goes for the one you told him to" leave it" repeat the "LEAVE IT" and try not to cover it, you want him to just leave it. But cover it if you need to. Again give a bit of treat and praise when he leaves the uncovered treat. I have a bunch of treats in my pocket (icky) or in a pouch on my side.
Once you can trust him to leave a treat and or toys and or shoes etc. its time to move outside. get a thin light rope that is about 10 feet long. tie it to the dogs collar, not a choke collar just a regular collar. have some treats on you. With the rope wound around your hand at first so your close to the dog, let him get by the chickens, if he does anything you are not happy about, like to much interest, chasing, barking, give a Stern LEAVE IT. Dont use the rope to tug the dog unless you have to. If the the dog eases up on the behavior, give him a treat. Then let out more rope ( ie: more freedom) after he is doing good and use the command and treat him and praise him. You can use as long a rope as you are comfortable with. I have one for training them the come command that is about 30 feet.
The come command is also a good one to teach along with the leave it command. All this will only take a week or two, then refresh often when ever possible. You don't need to have a treat later just go nutso happy with praise and petting when they follow a command you give them once in awhile. And when they know the command and do it with ease I dont really give any praise, like when they have to sit prior to going outside and wait for me to tell them they can go out after me. Its just something they know they have to do. But they do get a correction if they are excited and "forget" to wait. For a command like "leave it" if its something they know from experience that is not theirs like a childs toy or a sock etc I just say leave it, no praise really just the words. Something new to them like baby chicks when we have them ( now) leave it command and sit and down command and tons of praise. I teach they if they are very excited about something that they need to sit, and then they can sniff the item they are so excited about.
I hope this isn't to much info, and that it also helps.