aggression of our Jack russell

Are Jack Russell is about 11 weeks old. We've had him for 4 days and now am begining to wonder if we've made a mistake. The puppy nips and bites all the time and has shown aggression toward us. When we put our hand over his mouth so that he bites himself rather than us he becomes even more aggressive coming at us attacking. Is this something that will better over time or that dog training can help and how long are we looking at before we see improvement in his behavior? We also have cat's which he hasn't had a chance to get at but if he attacks us the way he does we are concerned about the cats too.

• Re: aggression of our Jack russell Mar 28 (0)