my 3 month old tibeatn mastiff is constantly biting when he plays or tugs at my pant legs when i walk around, its not that he is aggressive, he likes to play that way, but his teeth are sharp n they draw blood. will he stop biting when teething stops?? i have tried the yelping and withdrawing from play method, or holding his muzzle or giving him toys or treats to distract him, but nothing works. help