My 1 year old male goldendoodle, Seamus, has recently begun going to a dog park and has been doing great there with all the dogs. He loves to play, is not aggressive, and just enjoys himself there.......EXCEPT when one particular dog is at the park. When this dog is there, Seamus is terrified. The other dog, a male lab, tries to dominate Seamus the entire time he's there. He humps and barks/growls at him, but what really bothers me, is that he throws Seamus on the ground, on his back, and puts his mouth over Seamus' neck. He does not bite down, but this bothers me like you would not believe. This dog's owner lets him do it and my poor Seamus lays there and stares at me for help. What do I do?? Others at the park agree that this behavior is a bit much, and then others tell me that I need to let Seamus stand up for himself. Seamus will eventually go back at the lab, but the lab is bigger than Seamus and even when they start to play nice together, he still has the sole purpose of dominating Seamus. Seamus is rather passive, but I also don't want to encourage aggression, as my husband and I have nieces and will have children one day....If I let this dog be aggressive with Seamus, will Seamus become aggressive in return?? Please please some advice would be great!!