We have a lab mix that a was a 8 month old rescue/shelter pup when we got him. Now he is 2 years old, and although he has always played a little on the rough side, now he is running across the underground electrice dog fence we have and biting people. Luckily, we have always been outside when the two incidents have occured and the bites were not bad, but he looked upset and I had a hard time controling him. There was another occasion when we had another person get out of their car on our property an he bute them on their leg, he was barking and was really upset. I dont know what sets him off?? He gets pleanty of exercise and attention. We dont play rough with him, we try to use positive reinforcement with him and we think its working until he goes off and bites someone. I have owned many dogs and have never had this problem. We need help, If not we are going to have to give him up and we really dont want to do that.