My dog is a 15 weeks old Labrador and has been going out for walks for the last 3 weeks without many problems. But this week he has been refusing to walk. He gets very excited when he hears his lead being rattled, and is always pulling to get to the door, but once outside the gate he sits and refuses to walk. I've tried pulling him and he makes choking sounds until I stop then he sits down again! He gets very excited as I turn to head back home and pulls me all the way back to the door! Any suggestions?? Thank you