Hi there i desperatly need help with my dog. She's a mixed breed dog, i think she has german shepard and collie in her, i got her when she was already a year and a half old... at home shes lovely and sweet and not remotely aggressive but when i take her to the park she starts biting me, juming on me and nipping my feet. This only started a few weeks ago before that she was fine.. it doesnt seem to be aggressive more playful but yesterday she punctured my skin. its incredibly embarrasing as well. I dont want to stop taking her to the park but im actaully afraid to take her. Ive tried shouting and holding her down etc.. but its just getting worse...PLEASE HELP! if you have any advice please let me know.. thank you!