Hey i no now way an experence dog traniner but when our dog got nippy we did four things. 1)
We use bitter apple favor on our hands to create a bad taste for him. 2)
We kept a mist spray bottle near by to thing when he bit us(only when we could correct him right on the spot) 3)
we also made to loud "ouch" sound and stop playin or looking at him untill he sat down. *we say ouch instead of saying no because we say it alot even when were nornaly talking and dont want to confuse him. 4)
we try to just read the signs. if think he getting to routy when were playing with him we just back off now. and try again later good luck