Report this horrible person to Animal Control and if possible, have your parents video tape his activity.
One of my dogs wears a non-bark collar when he's in the back yard because he loves to bark at squirrels and not only does the barking probably annoy my neighbors, it annoys ME!
I purchased the collar from
http://www.gundogsupply.com
Don't buy a collar from Petsmart. I bought one from there and it's nothing but junk. I actually used it as a 'dummy collar' while training my dog to wear the real collar and this is something the instructions will tell you to do before your dog ever starts wearing the collar. The collar cannot be left on the dog all day because the prongs will rub sores on the dog's neck. The collar is very effective because it's a self-training collar. There are five levels of stimulation and my advise is NOT to use level five. It's too high. The dog gets stimulated when the dog barks so there is no association with the stimulation and the handler.
If the dog is not conditioned to wearing the collar, the dog knows when he's wearing the collar and when he isn't. He won't bark while the collar is on but WILL bark when the collar is removed. Like I said, the instructions come with the collar and must be followed.
Good luck and please report your parent's neighbor. Poisoning ANY animal is just cruel and uncalled for and he needs to be locked up.