I do not think you need to pay a professional. I have trained lots of dogs. Consistency is key. Do not ever let him get away with it even once without some sort of reprimand. You have to make it a big deal every time. If he doesn't like being tied every time he tries correct him firmly and leave him tied up for about 5-10 min. Then try again. The dog will begin to associate the chickens with discipline and learn to stear clear. If the dog doesn't mind being tied either tie him up where he can't see anyone (dogs are pack animals) or try a crate. Either way the dog has to associate something negative every time it tries. Don't wait until it's already digging start correcting him as soon as he even shows interest with a firm his name followed by no. If he ignores this then repeat the verbal cue again while ushering him to his time out. I have trained a PitBull that hated cats to accept mine. She still didn't like other cats, but eventually learned mine was off limits. I am now training my cat not to notice my chickens. Most of the time now she keeps her distance, but she is still tempted at times. I just make sure to correct her as soon as she starts stalking. It just takes time and patience