aggressivre rottie

Question
Hi,
    I have a 19 mo old rottie who is very aggressive towards other dogs(except our little rat terrier) and sometimes people(except anyone who lives in our house). His best bud is my 2 year old. Problem is that I'm very concerned that on a walk he is going to end biting somebody as he does lunge for people, and goes into a completely different state of mind when he sees another dog.
The last trainer he was with recommended a shock collar which seemed to do the trick except the dog knew when the collar was on and would act appropriately at that time.  I am hesitant to get a collar of my own as I've heard this can lead to heightened aggressiveness.  I've tried praise, walking and running for hours before introducing to other dogs and food rewards. Seems nothing is working.  I really love this dog and would hate to give up but I'm really concerned that he is going to hurt someone.  I got him at 6 MOS of age and don't know anything about his parents.  His name is Roscoe and any insight, help, or magic that you can offer would be greatly appreciated. Thanks

Answer
You don't mention whether or not your dog is neutered, but if not do that ASAP.  At 19 months, it won't change his mind set but as testosterone diminishes it will remove whatever role that hormone is playing in his demeanor.

Rehabilitating dog to dog aggression can be very difficult and requires a hands-on approach by a behaviorist, NOT a dog trainer.  THROW OUT the shock collar.  The dog will quickly learn that the approaching person/thing is the CAUSE for the SHOCK, and his aggression toward those approaching persons/things will GET WORSE; he will NOT learn to be more friendly toward the approaching person/thing.  Unfortunately, you hired a Neanderthal trainer with the skills of a chipmunk.  Take any piece of advice he gave you and FLUSH it.  

When offering any food reward, you need to KNOW what the dog is THINKING when it is being rewarded.  You may inadvertently be rewarding his thought regarding his need to defend himself against a person/dog or make a statement of dominance.  The same works for praise.  You need to be taught how to read your dog's body signals and how to reward appropriate body signals.  You also need an expert to observe your contribution to this developing problem.  Most owners offer a CUE to the dog (because the owner expects a problem and his/her body language and adrenaline rush cue the dog to act.)  In the mean time, as you look for a credentialed behaviorist, use a Halti collar or Gentle Leader, but do this with a strong martingale collar and second leash (NO CHOKE COLLARS FOR ANY REASON).  Do NOT lead the dog by its nose; use the collar/leash for that, use the Halti or Gentle leader to change direction (by turning his head in the opposite direction) when he spies someone or something that sets him off.  AS he changes direction observe him closely.  If he looks up AT YOU, praise him, tell him to "sit", food reward, and keep going.  You have a potentially serious problem developing here but it is not too late to change this dog's behavior.  I can't possibly instruct you how to do this in this venue.

As for your two year old child, your dog might very well continue to be this baby's "best bud" but your dog can also seriously injure this child faster than you can get up off your chair.  Do NOT allow the dog and child to freely interact.  Even the simple act of "disciplining" a human child by any dog (no matter how sweet and generally friendly that dog might be) can leave a child scarred for life, or worse.