I have a 3 month old boxer puppy, and she does the same thing! Usually, saying ouch and pulling your hand away works. Also, try redirecting; he can't know what he's supposed to be doing if you only tell him no, and you don't want him associating playtime with a bad response. Usually the best thing to do is just repeat the things you're doing with him, and he will catch on. Try to remember he's still a baby! I haven't owned a lab in a long time, but I know at least with Boxers, mine will have her puppy license until she's about a year to a year and a half old. Try to be patient and remember that some take more repetition to learn than others. :mdrmed: