St. Bernard Aggression

Question
I have a 22 month old male intact St. Bernard.  About a year ago he started to show signs of aggression to strangers, at this time we hired a dog behaviorist/trainer to work with him.  He has gotten much better and can even walk in crowds of people.  There are two things that he still does which are concerning to us. 1) He barks aggressively at strangers that approach him (we live in the city and people will attempt to walk over to pet him and when he sees them coming towards them he gives them a warning bark unless they have another dog and then he loves the person) 2) He senses people that are afraid of him.  We had an incident this past weekend with a person who is afraid of dogs, our St. caught onto this and nipped him the the back of his pants.  

We are trying to figure out what our next steps with him are.  Do you think neutering him would change these behaviors?  We had originally planned to show him, however with this behavior that option has gone away.  

Thanks,

Chris

Answer
The St. Bernard is a breed which should never, under normal circumstances, demonstrate aggression of any kind.  However, I have seen males of this breed with dominance and fear aggression issues several times in the past 15 years.

If you obtained this dog from a legitimate breeder as a show prospect, immediately notify the breeder of this behavior.  This dog's line should be removed from the breeding program.  Have your dog neutered.  While testosterone driven behaviors can be set by 22 months, the neutering experience will at least remove the physiological component.  Your dog, however, appears to be demonstrating a fear related aggression.  This is impossible for me to determine from the facts contained in your question.  However, fear related aggression is equally bad.

I have no idea what sort of behavior modification your behaviorist used; however, it appears not to have worked.  I suggest you get a second opinion from a credentialed behavior expert (NOT a dog trainer).  Since your dog has already bitten, and will bite again (nipping in the back of pants, legs, etc. is classic fear biting) you require an in-person evaluation and a careful re-socialization of this dog to approaching strangers.  Until then, do not allow strangers to approach this dog; do not walk him in populated areas.  Whatever is driving him (however it has been conditioned) will worsen and his behavior will escalate.  Fit him for a Halti collar (but do NOT use it to lead him around; use it in conjunction with a strong martingale and leash.)  This will allow you to control his behavior should a person inadvertently cross his path.  Do not correct him in any way if he barks/growls.  Simply STOP walking; the Halti will prevent him from lunging and/or snapping.  When the person has passed, regardless of what your dog has done or is doing, suddenly change direction quickly.  Praise the dog for coming along with you.  You do NOT want to praise him or interact with him in any way (including touching! speaking!) while he is reacting to the stranger's approach, since you may inadvertently be rewarding his fear response.

Find an expert and do it now.