Sorry, as much as I would love to be able to use the “big hara” line myself, there is no such thing. Not all fat is subcutaneous fat, so “sensei’s” belly may feel firm and still be due to that most modern of maladies; obesity. Here are two links to articles that should shed some light on where this fat is hiding:

From Wikipedia- “Greater Omentum”

From Wise Geek- “What is an Omentum?”