Spontaneous Agression?

Question
We have a 5.5 month male Golden Retriever.  He isn't easily scared, is great with other dogs and super friendly with people.  The problem is that out of nowhere he will start barking (showing teeth) and try to jump up on my husband/myself.  Most oten we are in the living room when this happens either sitting on the couch or telling him to get "off" the couch.  Our trainer has told us to keep his Gentle Leader and leash on at all times outside the crate.  It's helpful when we need to get him off of us, but I also think that he is frustrated with the leash.  The problem seems to be getting worse.  Could it be because he's entering teenage years?  Or do we have an aggression problem?  (We usually walk him at least 2.5 miles per day.  So, he is getting daily exercise.)  

Thanks so much in advance.

Answer
Dump the trainer, perhaps ask for your money back.  There is no way you should need to come here for help if you are paying a trainer.  A good private trainer is the best idea in some  cases.  Unfortunately a few of them have no business calling themselves dog trainers.  

It would be highly unusual for a Golden to be so hard to control it needs a Gentle Leader and leash in the house.  5.5 months is a little early to be using any training collar.  It sounds like the trainer has absolutely failed to address the issue of leadership.  The key to most behavior problems is approaching things using the dog's natural instincts.  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/

At any sign of aggression, you need to correct the dog showing you are top dog. Here are some ways of doing it:

''Elevation for small puppies:  Sit on the floor and gently put your hands around your pup's middle, below his front legs, and lift him up.  He is facing you.  Hold him for 15 seconds.  Repeat until he no longer struggles.  If he is past 10-12 weeks, lift his front feet off the ground, but don't pick him up.  

Cradling for small puppies:  Hold your puppy gently on his back, as you would cradle a small baby.  If he struggles, hold him firmly until he quiets for 10-15 seconds.  With larger pups, you can do this as your sit on the floor, with your pup between your legs.

Quiet lying down:  Place your pup on the floor on his side, with all 4 legs pointing away from you.  Use your hands on his neck/shoulder area and middle, to hold him in this position.  When he is quiet, praise him.  Lengthen the time that you keep him quietly in this position.  When he accepts this position well, handle his paws and muzzle, while keeping him quiet.''

The quotes mean this isn't my original work.  It is copied from my Puppy Raising Manual.  I have long used these or minor variations of them, and they are very effective.  You may want to give him a belly rub while he is on his back too.  Helps bonding.  There is a big difference between him rolling over and demanding a belly rub, and you choosing a time to roll him over and rub his belly.  The latter cements your place as pack leader.  

At that age, his testicles should be descending, and it isn't uncommon to challenge you for leadership.  Check with the vet about neutering him soon.