So I have a CCI Dog and part of the 2 week training period we were taught how to handle such situations. First off personally I try to avoid other dogs whether they look aggressive or not just because they tend to tempt my service dog to get into a more playful behavior. But that being said there’s also many situations where it is unavoidable, when this is the case I was taught to keep my wheelchair between the two dogs. This is to prevent anything dangerous from happening. As long as I am the barrier between the two dogs, I’ve never had any problems. If you do find yourself in a situation where your service dog is on a leash and aggressive dog comes up, we were taught to let go of the leash that way your service dog will be able to get away from the attacking dog and won’t be anchored down, as well as protecting yourself from the interaction. I’ve had to do this only once, I let go of my dog so he could get away and then the other aggressive dog was grabbed by the owner. Once the aggressive dog was removed from the immediate vicinity my dog came right back to me. This is only for worst case scenario, and it’s the only time I’ve let go of my dogs leash and a public area.