When returning from the dog park, my puppy (6 months old) constantly "goes on strike" and stays in down position on the ground. He doesn't react to treats, sticks or pulling the leash Any suggestions?
If the the dog's response to positive stimulus, as you tried, is wrong, you can do one of the following things:
Abandon him. Not really. If he wants to stay in the park, get out of sight. This makes the dog to focus more on you as leader, even when playing or running.
Negative Leash. If strength allows it, don't pull the leash. One strong and hard pull is more effective than a continous and soft pulling. You won't harm him.
That behavior comes from two sources. First youth and a whole new world to discover. Second, you are not training the calling in a proper way.
Please be careful. If you don't put the calling in his mind when he is young, you'll have inconstences on your adult dog, leading to probably some problems more.
Are two commands that the dog should response immediately because, in some situations, you could end up in a dogfight, a car accident or who the hell knows.