S.S.
I have a five year old boy who still has 'accidents' with defecation, although he has been completely potty trained for months at a time since shortly before his fourth birthday. I have a 3 year old (38 months) who can pee in the potty on command and usually does it himself (can go dry in a pullup for DAYS) - but sometimes decides whatever he is doing is more important, and soaks one. He does not poo in any sort of potty for any imaginable reward. :(
My five year old has to wash his underwear after accidents, my 3 year old still wears pullups.
Good luck.