It's best to educate dogs not to fight. If you hit them hard, they will be afraid of you, and then they will not come near you. If you hit them gently, they will think that you are teasing them and can't achieve educational effect. It's best to scare him with sound. What dogs fear most is a sudden loud noise. You can call him. Pet shops have "click devices" for selling pets. You can try. Click on him as soon as he comes out.