We are potty training our son (2.5 years old) and he has made great progress. He is at the point where he very rarely has all-out accidents (where he soils his pants) and he will go independently while playing. The issue we are having is that he will say he has to go potty and will go to the potty but many times (several times a week, if not daily) he has already gone slightly in his underwear. Just enough to leave a small quarter size damp spot on this underwear but not to soak through to his pants. Oddly he seems to do this more often when at home then when he is out at other peoples homes or out at stores etc. What types of things can we do to discourage this?