We are SO pleased with this bark collar! I would give it more than 5 stars if I could. We've had it for a few months now. We adopted our 2 year old great dane when she was 6 months old. Her nuisance barking has improved since we adopted her, but was still a problem that we had not been able to remedy with training or other bark deterrent products. She would not only stand at the fence and bark at people and dogs who walk past our house, but when we invite guests into our home she would bark at them for up to 5 minutes until she got used to them and felt comfortable enough to calm down. I didn't know how well this collar would work on an extra large dog, since I couldn't find any reviews of people using it on their great dane or other really large breeds. And our dog is a little nervous around new people, so I really wondered if a bark collar would be a good idea or not (or whether it could possibly make her more nervous), but she is a big dog and her barking can really scare some people who aren't comfortable around dogs, so we decided to test it out. We followed the instructions exactly, and used the setting where the shock level reset at 1 again each time. It worked! It didn't prevent her from ever making noise (which isn't what we were trying to do -- we're ok with our dogs letting out a couple short barks to alert us to someone at the door or a stranger approaching, we just wanted to stop the incessant barking problem). The first day we used it, after 2 or 3 barks she definitely noticed the collar and quieted down. It started working quickly, and has worked consistently since we got it. We did follow the instructions, and remove the bark collar every night (although there have been a handful of nights we have forgotten to take it off overnight, with no apparent negative effects). The best thing about this collar, is that it has not only improved our dog's barking habit, but it has improved her other behavior too. As I mentioned, our dog is a little nervous when meeting new people. Especially men. Or anyone with a beard, or wearing a hat, sunglasses, a large coat, or carrying anything large in their arms. Basically, she's a big scaredy cat. Since the day we adopted her and brought her home, she has been really afraid of my adult brothers and my father (even though they are calm people who have experience around dogs). My dog will bark at them and run away from them every time they come over to our house, no matter how much time they spend letting her warm up to them or offering her treats. But since she's had the bark collar, she doesn't act totally scared of them anymore. She may still approach them slowly at first, but she doesn't bark, usually doesn't run away, and she will even go up to them and let them pet her on her own now. The only thing I can figure is that the barking used to get her so worked up that she was then even more anxious around them, and now that the barking has significantly decreased she doesn't get so worked up in the first place, so she can relax around them a lot easier than she used to. It's really amazing that this one little collar has made such a big change in our lives with our sweet scaredy cat of a great dane! I chose this collar on the recommendation of a friend, and because we have two dogs, so I didn't want the dog wearing the collar to get shocked if the other dog ever barked (we previously tried a different bark deterrent product from the local Petsmart store, which let out an ultrasonic deterrent sound everytime the dog barked. Unfortunately, we noticed that product also made the sound when the other dog occasionally barked, or when the kids were noisy, or when the kids practiced the piano. We had to stop using that one quickly!) This collar, on the other hand, works great, I don't think she's ever been shocked when she was not barking). Oh, and I should also say, about a month or two after getting the collar we switched to using the setting where it starts at the level that it left off at the last time when the dog starts barking again the next time. That's because our dog has learned that she can make lower pitched/quieter little barks and they won't trigger the collar, but then if she raises her volume at all it will trigger it. Once we switched that setting, it has consistently continued to work well for us. It's not a way to silence a dog. And we're ok with 2 or 3 short barks to let us know there's someone approaching us. But this has all but stopped the barking at people over the fence, barking at our neighbors when they are in their back yards, barking at people who we invite into our home, etc. (Except on the couple of days when we have forgotten to put the bark collar on in the morning. Then we quickly remember to put it back on again). :)