My puppy is nearly 12 weeks now and altho ive followed yr advice from before weve still got a real issue with biting. I cant trust him with my son and hes ripped/snagged numerous trousers and skirts of mine and my parents. Ive had advice from my trainer too as just started training him but just dont know what to do anymore. He also chews the sofa all the time. Ive tried the bitter apple stuff and it doesnt work!!
Any ideas my knowledgeable friends?

Is he chewing the sofa when you are in the house or just when you are out of the house? Crate training him until he is older and out of the teething stage would be a great solution if he is doing it when you are out of the house. If you are in the house then the only option is to take him away and give him something proper to chew on (raw meaty bone, nylabone or a stuffed kong frozen for his teeth and gums.) and be completely consistent. You have to remember that he is very young and he only has his mouth to explore things.

With regards to biting your trousers when walking, firstly I would say get bicycle clips to wear around the bottom of your trousers so there is no 'flappy' bit for him to grab onto. Then when he DOES do this behaviour, stop dead so it is boring for him, and then distract him with something else. He is a very young puppy and he will soon learn. What you do need to do is teach him that other behaviour is more rewarding and more fun than the behaviours you don't want.

Do you have a baby gate in a room where the dog cannot make any mischief? He needs a time out when he gets so excited he rags on your trousers.

I agree with Josh that pup is still a baby and life is so exciting, and chewing the sofa is such great fun. He doesn't do it to annoy you!  Distraction is the best tactic given that he is so very young.  Wait until he's a bit older, and the chewing starts in earnest when he's teething. 

Remember that he does need far more frequent attention than an adult dog.  You need to make sure that you are more exciting than the things that you don't want touched.

I use a ball - one of those open mesh ones - if mine starts going for my legs/ trousers - I throw the ball ahead - the ball is good for a game of tuggy then if he brings it back.  I also find that mine will chew a mat or something else that I don't want him to - when he wants attention.  I have quite a few things for him to chew - if I am busy I offer him something I allow him to chew on.  If he persists he gets time out in his crate for a short while.  Distract from bad behaviours and praise the good ones - lots of praise!  

I have a positive interrupter trained with my 16 week old, at 12 weeks when she arrived here she was an absolute sod for biting feet/trousers/ankles etc!

Basically it's a signal that distracts the dog quickly, so you can then give them something else to do.  I trained it like this:

http://www.youtube.com/watch?v=TBvPaqMZyo8 (vid from Emily Larlham/Kikopup, fantastic positive trainer)

It's been brilliantly useful for so many things, and the housemates are using it too as she's still a bit chewy with their feet (spends much less time around them so less learning opportunities so far).  Once she was distracted I could give her a chew, or a toy, or play a game or do a bit of training or even just click/treat for her stopping biting and looking at me, and I could then click/treat for her continuing to not munch me (even if it was just for half a second after she's stopped, it gave me something to build on).    It worked very well, with c/t her for not going back to bite once I'd interrupted her she was stopping herself more so I could add a cue ('no biting' for her, but whatever you like), and now I can just give that cue when she starts and she stops straight away (again we then go and do something else as a reward).  She barely tries now, I think she's tried once in the last week.

That was a good video and many useful techniques, very fond of the Kikopup tutorials.

My nine week old GR pup has some bitey moments usually when she's getting tired, and grabs at flapping trouser legs and feet when you are walking. I had been using distraction to dissuade her, but that video demonstrating a distraction noise is very useful. Will start teaching her this when she wakes up!

Love the Emily Larlham videos and advice - that is one very good tip I have got from CD.  She has her own web page - dogmantics.com