Not sure what you could do. Mackenzie is just TT's (like 3 weeks) but for poos, what seemed to click for her was she gets a chocolate and sticker everytime she does poos on the toilet. (she only usually does one a day and the chocolate is the size of my little finger nail). I find she is doing really well with all the TT stuff but if she in engrossed in something (like palying dolls or TV) then she just won't go to the toilet even though I know she is busting. When I know she needs to go I just gently guide her to the toilet and she seems to go. I know this probably dosn't help but is your DS holding on for hours and just 'too busy' to go or is it a confidence thing. I'm sure if he is still doing this in summer it will be over with in no time when they can all run around naked! Bring on summer!