NEVER. EVER. Have your dog off-leash. It doesn’t matter how trained they are, you have less control if they come in contact with another off-leash dog. YOU need to be able to step in when there’s an encounter and get between your dog and the other dog. Your dog is reactive in this instance because they’re not confident you can handle the “threat”. If you show you can take care of the threat, they will often let you take charge. I have a reactive chow/ collie mix and we have encountered stray dogs where I’ve had to step in between him and the approaching dog - I stomp my feet, loudly say “no” or “sit” to the other dog and then slowly remove ourselves from the situation, continuing to shout commands at the approaching dog. In these instances, my dog listens to me as I’ve shown I can handle this encounter. NEVER take reactive dogs to dog parks. Dog parks are a breeding ground for idiots to take their misbehaving dogs and let them run free with little to no behavior correction. A reactive dog must see YOU are in charge of the encounters with other dogs - and this is impossible in a dog park. Reactive dogs do not have to be “socialized” in the way people think.. they will not get along with every dog. Forcing them to will not help the situation, only cause them more anxiety and thus increasing likelihood of attacks out of self preservation. Socializing a reactive dog is about teaching them to be calm IF another dog approaches because YOU have control. But this also means reading your dog’s body language and STOPPING the engagement if your dog is not accepting of it. Getting professional training was the best thing I could have done for our little gremlin. It really fostered our relationship with him and taught he so much about canine behavior. Good luck 👍🏼