This sounds like a pup with very high prey drive. That's a good thing though!! Dogs with high prey drive can often make great search and rescue dogs, protection dogs, etc. I'm not one of the more qualified people on this board so look for info from some of our other members like Lisa. She's busy this weekend though so I'm not sure if she'll be on here right away. The pup should always be supervised, and obviously you will have to give a firm "no" to any undesirable behaviors. My AB puppy bit our pant legs and chased our cats until she was maybe 3 or 4 months old. We were persistent with the corrections and made sure she was never unsupervised with the cats. Now she no longer chases the cats, but we still ALWAYS supervise. The pup doesn't sound agressive to me, it just sounds like he has a lot of prey drive.