Hi, I'm struglling to teach my 4 and a half month old male GSD puppy to fetch. At home he shows interest (sometimes) and will fetch thrown toys. He brings them back to me most of the time and waits for the next throw. When we are outside at the beach or at the park, he shows no interest in playing fetch whatsover. Does anyone have ideas how to interest him in playing fetch outside? I'm just looking to get him more exercise, beyond walking. Thanks.