We just had a thread on barking not too long ago.
http://www.bigpawsonly.com/index.php/topic,4490.0.htmlI personally would use correctional collars as a last resort. Shake cans, squirt bottles, ignoring, etc.. combined with treats usually can work just as well.
And this may sound weird, but I would use a static collar on my dogs before a citronella one. The best of those type of collars out there have several different levels of stimulation and you are supposed to set it to the lowest level that works for your dog. I've tested one before and it felt like a static shock you'd get from a carpet. I don't believe you should put something like that on your dog unless you've felt it first. JMHO, fair is fair. (And yes, I did also try a prong on before putting one on my dog. I thought it was much more gentler than a slip/choker collar)
On the other hand, Citronella collars I've seen only have one level, "ON". The citronella can get in their eyes, mouth and nose and linger there. It is a lasting correction. Think about how it feels to have something in your eyes or a bad taste in your mouth. Or even worse an unpleasant smell and then multiply that by goodness knows how much, since dogs' sense of smell is so much more powerful than ours.
I'm sure that many people disagree with me and that is ok. I'm just telling how I came to my decision on the matter, not saying its the best way or THE right way. Just how I decided for myself.
Good luck and try to think of it from the dog's point of view as well.
~moni