You wouldn't want to actually wait until the dogs were engaged in fighting before using the e-collar, Michelle. The e-collar would be used to prevent the aggression that would then escalate to a fight.
I successfully used the e-collar to cure my dog's dog-to-dog aggression. I couldn't even take her out for a walk for fear that we might encounter another dog (on OR off lead) and she'd cause a scene and maybe end up hurting the other dog if it did come close enough to make contact with her (she's a chow/pit cross). Muzzling DID ensure that she couldn't hurt the other dog, but it didn't solve the problem of her aggression towards them, and people automatically assumed she was generally unfriendly (which isn't the case - she loves people) and would steer wide around us and even make comments. Because of her breed, I did not want to continue down that road, and decided it would be best to see if we could teach her that aggressive or dominant behaviors towards other dogs was not acceptible.
I decided to consult a trainer who had experience with dog-to-dog aggression, since I had no experience with aggression at all. We began with the prong collar, but because it took such a forceful correction to have a positive effect, decided to switch to the e-collar. She probably required a level 8 or 9 correction, as Ed would put it, with the prong. Anything less than that would actually make her aggression towards the other dog escalate. Another reason for switching to the e-collar is because most of our work was done at the dog park, outside the off leash area, and we were getting all kinds of dirty looks and nasty comments for having to correct so hard with the prong. We used a Dogtra200NCP. Her normal, daily working level (the level at which she *just* feels the stim) is around 25. The level we had to work her at for dog aggression was 40. When she was aroused by other dogs, somewhere between 35 and 40 was where she could *just* feel the stim, but that didn't do much towards getting her attention, so we bumped it up to 40 to make sure she understood that she was being corrected. Even at this level, she did not panic or vocalize continuously when the button was pressed; but she DID know it didn't feel good and immediately stopped her behavior when she felt it. I zapped myself at this level and it isn't pleasant - it feels like someone pinching the snot out of you! But I wouldn't use a level on my dog that I had not felt first.
Along with the corrections for showing aggressive behaviors, we also conditioned her to the clicker and used it, lots of praise, and treats when she was not being aggressive or dominant. We praised her for looking at or showing interest in the dogs on the other side of the fence, or dogs being walked on leash at a distance, but the second she tensed up and hackled, growled, showed her teeth, barked at, or lunged at them, she got strongly corrected. Immediately after the correction, though, we became happy again. Verbally praising her most of the time, and adding in the click & treat when dogs were right up close to her at the fence. She got rapid fire click & treats for face-to-face greeting of the dogs through the fence, and if there were multiple dogs over there (which there usually was by the end of it because some knew what the clicker meant and were eager to get a treat from us!). We also praised, clicked & treated her when dogs in the fence got into a skirmish, as long as she didn't pay it any attention.
It took about 2 months of going to the park once a week, and working daily with her at home with her basic obedience, and my goal was simply to be able to take her for a walk and not have to worry about encountering other dogs, but now she can even play with other dogs with no incident. The trainer felt confident that she would even be fine inside the fence at the dog park, so for our last session, we allowed her to go in and play with them. She still had the e-collar on, just in case, but she knew what the correction was for and how to respond to it now, instead of thinking it came from the other dog and going for him, so we weren't worried about her attacking another dog if she got a correction. We did have to 'remind' her a time or two when she started posturing towards a big Malamute, but other than that she did great. I don't take her to the park or allow her to play and socialize with strange dogs, but the fact that she CAN without incident makes me feel more confident about taking her out.
The e-collar can be used successfully to help diminish or eliminate dog-to-dog aggression, but your dog needs to know and accept the fact that you're in charge first. Working the dog daily in obedience is one way to establish dominance over your dog, and it also helps to grow the bond between you as well. Obedience should be in place before attempting to remedy dog-to-dog aggression, in my opinion.
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