Please don't give up on the dog park. Perhaps you could take him early in the morning before a lot of people show up. That way Duncan can walk around and sniff around and get a feel for the place. Perhaps he was just feeling unsure of himself and his surroundings so he acted out by being agressive. Also, if there are too many dogs, he may have been nervous. I go to a dog park (about 30 miles from my home) every once in awhile with my 20lb terrier Fenway. I know not to go on a Saturday afternoon because there are too many dogs there and it's nuts. I go early in the morning when there arn't too many dogs and it's more "calming". As far as the person who said "that's why I don't rescue dogs". Crap on her! She's an idiot! Anyone with a brain would know not to say such a stupid thing! Ignore her. You'll find at a dog park there are MANY nice people but there's ALWAYS going to be someone who's going to be weird or mean. Just ignore them. They're not worth your attention! Perhaps you can find a doggy day care and see if they have a play group? I know a doggy day care in a city next to my town USED to have a play group meet every Saturday. It cost $8. I believe it was for 1 hour. Look around. Perhaps you could find one. Take him there for about 1 month everyweek and then try the dog park again. Just a thought. Good luck.