I have a similar problem with a 6 month old Border Collie. He knows all of the commands, sit, stay, down, leave, come etc but he's suddently decided to only do them when it suits him. We've only had him 6 weeks and he's on his 4th week of puppy training class and I'm beginning to wonder if it's worth it. He's more obedient at home than in class although it's good for him to socialise with other dogs. I sometimes feel as though he's misbehaving on purpose. I do struggle to not shout at him when he's naughty, but sometimes it seems to be the only way to get his attention. I tried a whistle, but he even ignores that now.