I adopted a mixed breed dog from our local animal services shelter and it was quite a bit to nurse him back to health - sometimes I see his old pictures and cannot believe that he is so healthy now. From the beginning, he has been very affectionate with everyone and loves to play with other dogs. BUT, if a dog his size or bigger gets too close, he goes on attack mode and I cannot control him - this happens with 90% of big dogs regardless of gender and passivity. I can keep him controlled on all situations other than this one. When he get's like that I have made him sit, tried to distract him, made him lay down, taken him for a walk to try to reduce his energy level, given him treats, petted him, talked to him in a harsh tone, talked to him in a soft tone, etc. I've tried it all separately and in combinations to no avail. He is a mid-sized 30lb dog and some dog parks require him to be in the big dog section. The closes park to our house has a pond that he loves to swim in, but dogs of all sizes roam there and I am always cautious when big dogs get too close. Most of the big dogs at that park are very sociable and many of their parents have tried to help me calm him down and get used to their big dogs, but again, it does to work and often times I would have to leave the park. On a couple of occasions, when I tried to remove him from the other dog, he has actually tried to bite me (got me once). I don't know what to do. Any tips or advice on how to get him to be friendlier with the bigger dogs?