My Puppies behaviour

Question
Hi i have recently bought a beautiful male cocker,he is only 13 weeks old but as time is going on is getting more and more aggressive with me and my family.  He is continuously biting at us for no apparent  reason even when we are trying to show him affection.I have explained this to our vet and he said to wait and see if this continues i have organised for a dog trainer to come to my house but i am very worried that if his behavour continues to get worse that i might have to put him to sleep as i do not want to bring an aggressive dog up. I would greatly appricate it if you had any tips for me.  
Thanks a lot Alison

Answer
If you checked my profile for Cocker Spaniels, you saw I didn't claim to have much experience with them.  I can't say if such biting is common to Cockers, it definitely is common in all the breeds I have much experience with.  It is also a common question here and other Internet sites.

Young Labs, which I know best, and other puppies tend to very bad about
biting.  You see a litter of them, and all the ones that are awake are biting
another one or themselves.  I am not even sure they realize that when they are
alone, if they quit biting, they would quit being bitten.  At 3 to 4 months
they are getting their adult teeth, and it seems they spend every waking
moment biting or chewing.  I maintain a Lab's favorite chew toy is another
Lab.  Otherwise they settle for any person they can.  They keep hoping to find
one that won't yelp and jerk their hand away, or growl "Bad dog." and clamp
their mouth shut.  Then offer a chew toy.  They keep trying despite hundreds
of corrections.   Another good technique is to quit playing and go away.   Be
sure to praise them when they are playing nice and not biting.

You just have to keep on correcting them, hundreds of times, not dozens.
Provide sturdy, safe toys such as Kongs and Nylabones.  Avoid things they can
chew pieces off and choke on them.  Keep them away from electrical cords.
Crates are essential for most young Labs and other dogs.

The pet stores are full of toys that many dogs will quickly chew up into
pieces they could choke on or cause intestinal blockages.  If you are not
there to watch, stick to sturdy stuff such as Nylabones and Kongs.  Keep a
close eye on chew toys and quickly discard anything that is coming apart in
pieces.  Rawhide is especially bad because it swells after being swallowed.
These problems are the worst with, but not limited to, large, aggressive
chewers such as Labs.

I had a trainer from a service dog school here today.  She was talking about how she frequently ends up bleeding when she pets a little puppy.  What makes a good trainer is patience, consistency, and self discipline.  What you are fighting isn't aggression, but only normal dog play.  No way should you have to destroy him.  He will grow up with the affection the Cocker Spaniel is known for.

Start obedience training now too.  Keep the sessions short, only a few repetitions at a time.  A few minutes her and there, and in a few months, people will be impressed how nice he is for a young puppy.  A professional can only teach two things, the dog to obey him, or teach you to be top dog.  The dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog.  Life is much easier if the 2 legged pack members outrank the 4 legged ones.  You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/