Thanks Annie for the suggestions. We can see some improvements these days... as his incentive plan is on work big time. He is keen to get more n more rewards on each good day... which is without potty in pants.
we would observe him for next 10 days more & then take a decision on seeing a doc.
I agree with Annie, its time to see a doctor. This link gives you lots of information that should be helpful.
http://www.practicalgastro.com/pdf/November02/LoeningBauckeArticle.pdf
It is probably a physical issue, a dysfunctional colon and lower intestine. Please look up encopresis. If the child is seemingly not aware the poop is coming out, that is probably what he has. It is NOT within his control and you cannot shame him out of it or punish him out of it, doing so only makes things worse. Please talk to his pediatrician about encopresis, and if the pediatrician does not know much about it (which is unfortunately rather common), ask to see a pediatric gastroenterologist. It takes time and care to heal a colon that is not working, but it can be done.