Lab attacked my Newfoundland

Question
QUESTION: My 4yr Lab attacked my 6 month old Newfoundland dog for no unexpected reason leaving my wife to take the 6 moth old to the emergency room where he had to receive stitches too 9 diffrent puncture wounds on his throat.
Lab has never done anything aggressive at all before.
Im worried that my dog is dominant over my wife since ive Deployed.
They use to play all the time and this never happened it was as if they were best friends.
Why would my Labrador do this?
Is there a throat guard that my puppy can wear for better protection in case this happens again?

ANSWER: I would neuter both of them if not already.  At 6 months the Newfoundland is maturing, producing hormones, and may have subtly challenged the lab.  The situation my be out of hand.  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/  For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm  Both dogs need to learn to submit to your wife.  This may be a case where a good obedience instructor could be a big help.  Some of them are useless or worse.  

The classic spiked collar is meant to protect a dog's throat from other dogs and wolves.

---------- FOLLOW-UP ----------

QUESTION: Bruno (lab) is fixed Rowdy (newfie) has an appointment on July 2nd to be fixed---I tried introducing the dogs to one another again w/bruno on a leash (rowdy cannot wear a collar right now and his injuries were also rubbed by the haltie)---they seemed fine --rowdy was kissing and so happy to see bruno-playfully jumping -they were laying on either side of me late on and with out warning (all toys and bones have been removed from the house) no growls or anything bruno attacked rowdy again---I was able to get him off luckly by getting in the middle and bruno bit me and this let rowdy get away
so for now we have them both seperated at all times and rowdy does have alot of seperation anxiety now--but I am trying to split my time equally between them and take bruno on long walks each day (I cannot walk rowdy due to his injuries right now)
is there any hope that after rowdy is fixed they will be friends again----until 4 days ago there were no problems---since then there has been 3 attacks---leaving rowdy with several puncture wonds and lots of stiches and myself with stiches as well  

Answer
Once Rowdy is fixed, Bruno may, at least once all the hormones are gone, may again see him as an unthreatening puppy.  Rowdy may not crowd him either.  I can't promise anything.  If they both have a high drive for dominance, neutered or not, they may always be competing.  You will just have to see how it goes.