I agree with the PPs - why not meds and more exercise? Have you tried a bark collar? Like the PPs, our Lab mix is highly reactive if he's not well exercised. A single long walk a day isn't enough. He has have at least a 3 mile run and a 45 minute walk (or another 3 mile run) every day - and he's 8 years old. As long as he gets that, his barking is far more manageable. He's got a high prey drive that we ended up using an e-collar to manage. We worked with Off Leash K9 trainers
http://www.offleashk9training.com/.
Oh, we bike with the dog to get him his 3 mile run. It goes pretty quick. We do it rain, snow or shine.