These recommendations are totally unbiased. I do not advertise on this blog. I am giving links, but I get nothing if you make a purchase. I am receiving no compensation whatsoever for this post.
By the way, these tools are not just useful on your own dogs. Some can be used to protect you from other dogs in the neighborhood or to help a neighbor's dog see the error of his ways when barking non-stop all night.
Tools Using Sound
I wanted to avoid things that inflicted pain. I read in a place or two that using shock tools when trying to stop aggressive behavior is not a good idea. It can backfire and increase the aggression. Sound, on the other hand, works pretty well. With all of the sound tools, I first say NO as a warning, then follow with the gadget. After a while, the tool sound becomes less and less necessary.
Dog Dazer II Ultrasonic Dog Deterrent - This is one of my favorite tools. It emits a high pitched sound that humans don't hear. It does NOT work on small dogs. It works great on all of mine. I point and push a button and my dogs stop what they are doing and look my way. I like that it's discreet. People have no idea what I'm doing. If you are out walking your dog and an ill-mannered dog approaches, you can "dazer" him and he'll likely back off. You can do this without the owner knowing what is going on if you are one who likes to avoid confrontation.
Pet Corrector - I call this one "the hisser". It makes a loud hissing sound. It, too, is an attention getter. I go back and forth between this and the dazer. Dogs can learn to ignore a sound if it is overused. Swapping around is good. I ordered a two pack of these. They are good to have in different spots around the house. I think I remember reading that each cannister is good for about 50 hisses.
Dog Horn - This one is loud. If you use this with the neighbors dog, there's no hiding it. I use this when my dogs are further away OR when George's behavior is particularly bad. I will probably carry this with me when I go hiking as well. It can be uses as a distress call. Some people have successfully run off bears and coyotes with it.
SprayShield Animal Deterrent Spray - This is described as "a citronella based spray tested and found as effective as pepper spray without harming the dog or making them more aggressive." I have not used this one yet and hope George learns to behave before I feel the need to try it out. I got it in case a fight ever got out of hand.
MaxxiCalm - This is a vitamin type chew tablet that helps reduce stress. You can see the main ingredients on the bottle - all are things seen often in vitamins for humans. I have been giving George 2 or 3 tablets a day and it seems to have made a difference. I am now giving it to Annie, my dog who worries and is stressed when I am gone too long. I haven't been using it with her long enough to know if it's helping. I also bought Bach Rescue Remedy Pet, based on positive reviews, but haven't used it yet.