
Hi,
I have a young dog who used to do some thing very similar. (I say used, but he still would, i just know how to stop him these days).
Dont rush out and get him neutered just yet, that could in fact make him worse. If he loses all that testosterone, he could lose a lot of his confidence, which might in turn make him more aggressive with passive dogs.
My Rocky was brilliant, until i had him done, then he hated dogs, but notably, just the ones that he didnt really think where a big threat to him. He wouldnt put up with any kind of aggro, from the smallest of dogs, which he used to ignore, and very nervous dogs would also get 'shown who's boss'. That said, he would ignore any dog he felt capable of doing him serious harm, as long as it didnt challenge him!
If you think that neutering may help, ask your vet as there is an injection that will temporarily do the same job. If you try that and it doesnt work, then dont get him snipped. If it does then consider the snip.
I now prevent Rocky from being a git in several ways. I try not to walk him in confined areas, such as narrow paths etc, I have seriously im proved his recall, and also got him very toy orientated, so he really wants teh ball i keep in my pocket. He now knows, that by sticking by me when he sees another dog, he will get the ball game he wants.
Emma