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We have an 18 month female Jack Russell. She literally is the sweetest dog -- She is good around all the small children in our family, she plays well with all the dogs in our family which include small and big dogs, and she goes to doggy daycare once a week and is fine. However, when we take her to the dog park, she is really aggressive with other dogs, whether they are coming up to smell her or just want to play with her. She thankfully has never hurt another dog beside a scratch or two, but I still feel bad and want her to be able to play wherever we take her.