Aggressive chow with other dogs
I have a 2 year old chow who has been socialized with every dog park,since the age of 12 weeks old and goes to Starbucks practically every day. Loves people and gets along with children as well. He is petted a lot by strangers and seems to love the attention. However, he now is showing signs of aggression towards other dogs. Every day a sweet lovely dog comes to play with my chow. The dog slipes under the gate to come in. I have almost 2 acreas of land for them to run around on. They have always gotten along very well until now., in fact, my chow would sit down at the gate waiting for his friend to come play. My chow is now trying to fight with this neighbor dog. The dog is trying to get away from my dog by running away. Why is my chow showing aggressive behavior with this other dog and what can I do to stop it?