K.H.
My youngest son was the same way (my other boys were potty trained by the time they were 2). When I spoke to his dr about it, he told me that potty training was for the parents, not the kids and that once the child gets tired of having messy pants, he'll sit on the toilet. Well, my son finally began sitting on the toilet at age 4. I know it's a hassle, but I think the dr was right, and for me, it ended up being less of a hassle to work on my son's schedule than mine.
BTW - my son who I'm referring to saw me write this and told me that he remembers that he was afraid to sit on the toilet because he thought something would come up and grab him - no idea why he thought that, but he did. He never expressed that he was scared at the time. I just thought that was interesting that he remembers.