Mastiff vs. 3yo Human

Question
Hi!  About 6 months ago my family rescued a 220lb Mastiff from animal control. He is sweet and docile, kind to the cats, and really close to being a perfect pet.  The only problem is that every now and then, 4 times in 6 months, he will bark and sort of lunge at my 3 year old.  He did that to me twice in the first days that I had him if I startled him while he was sleeping, but never without provocation like he does with my son.  The 4 times he lunged at my son were: when son was walking past with a batman mask on, two minutes later without the batman mask, once when the dog was laying with his head on my lap and my son was playin on the exposed part of my legs (without the dog head, which is huge), and this last time when I asked my son to wipe the dog's (name is Bujakacha- sounds like boo ya ca sha) jowls (he has enormous jowls and drools a lot).  Our vet said that the dog is jealous, the dog is very attached to me, so she suggested that my son become more active in his care and feeding so that he appeared to be the master.  My son is three, there is only so much I can get him to do.  He loves Bujakacha but he is a little kid.  I don't know how to handle it when he does this, I usually just yell- a lot, and put him outside, however, the dog weighs twice as much as I do and I can't always get him outside, so sometimes I just yell.  He is a good boy other than this, but because of his size it is scary for everyone.

Can you tell me how to handle this, or better yet, how to prevent it?

Thank you for any suggestions.

Kate

Answer
I think the best thing you can do is to call around and find a trainer that can come to your house,so the trainer can see what is going on and address it right away,as this cn become a dangerous situation if left untreated

A trainer like that is your best bet,and explain to him/her the exact situation-then you can work on the best problem.A trainer is the way to go,as they can see what is going on and find the best way of correcting it