Potty training woes with a three year old boy?

some days he'll go to the potty all day and we're all happy! others he is just too busy to care. and he NEVER will poop in the potty. i give him rewards and praise when he goes, but that hasn't worked yet. its time for him to go potty! i mean anytime a kid tells you mommy i pooped please chance me, i feel he can sit on the potty and do it, but he won't.........and if you are just going to suggest i him don't bother to leave a comment b/c that won't work!