It seems to get exponentially more difficult to lose that last bit. I haven't conquered it yet myself but it's coming along, little by little. My methods might not be the most efficient, but they are paying off. It may be easier to explain what doesn't work for me--sit ups, crunches, and repetitive exercises. Abdominal exercises got me nowhere.
Basically I play sports four times a week, do some sprinting, do Mark Sisson's "five basic movements" on days when I'm not playing, and IF from time to time (mainly on days when I'm going to be playing). After I play, I eat my main meal and relax. If I'm not in the mood to exercise, I don't.
Then, through no intention, but due to the fact that my daugter is in another state, I don't play any sports and have more of a regular 2-3 meals daily routine for about four days per month (when I go for a visit). When I get back home, it's back into my asymmetrical eating/playing/exercising "unroutine."
I've been going through fat burning/plateauing intervals for about 2 1/2 years and this last bit is no different, it's just that the pace slows way down. I believe incorporating more heavy lifting might help me kickstart things. I aim to start that next year, as soon as I can find some good, cheap weights through garage sales/Craigslist, etc.