Please get a trainer who is certified. Ask if they are Delta Society or Canine Good Citizens.

Some organisations like Bark Busters do not train the trainers... you pay to enter into the franchise. So you may get a good one, and you may not. Its luck of the draw. Its much better to find someone who has accreditation to help you.

Problem barking is very hard to work at. Citronella will work while its in use. What I mean is the minute the collar is off, the dog will bark again. Some techniques you could use is to go to the side of the fence with the large dog and have a water pistol or a hose... everytime your dog barks, spray it.

Or do training in your back yard away from the fence. 3 times a day for 5 minutes max. Get your puppy listening to you while outside. Every 2-3 days move 1 meter closer to the fence. Go slowly, if your puppy starts paying more attention to the dog next door, move further away for a few more days and then inch closer. The goal is to get your puppy more interested in what you are doing, than what the other dog is doing. Keep a water pistol or bucket of water close by to douse your puppy when they get into the fence frenzy.

My dogs do this at the front yard sometimes, they LOVE chasing dogs who walk by and go nuts and think its the most fun ever. One of them sparks it off and then they both think its so much fun. I let them out the front for an hour a day now, so they can have their fun and then they are put in the back yard... I haven't the time or energy atm to be training it out of them