Most of the advice you have been given is pretty good, but here is something else you can try. I have been advising this in my puppy classes for some time and the feedback I am getting is good.

Find something which your puppy really doesn't like the smell of. It might be some kind of food preparation. Everytime your puppy does this, let it sniff the thing which it finds unpleasant, so that you are taking the fun out of what it is doing.

One person I know discovered her puppy didn't like flea sprays, so she showed it the container everytime the pup grabbed her, so the puppy stopped the behaviour after a few repetitions.

Someone else discovered that their puppy couldn't stand the smell of tomato ketchup, so they showed the puppy the lid of the bottle everytime it grabbed at their heels or clothing and this stopped the behaviour.

Yelling no, or yelping as if hurt can stop some dogs, but for those who really are into nipping from behind and hanging onto clothing, a smell of something they don't like can be really effective.

I speak from personal experience as all positive actions just got my puppy laughing at everything I tried. Eventually I discovered that the smell of Lemon/eucalyptus oil put him off!

Fransetter