There were many people practiced Shen-gong in Malaysia in the 70's and 80's but the popularity of such has seen a decline now days.
I can still recall that there was a Shen-gong sifu who was also a bread seller outside of my school. Let's just call him Uncle Lim as I have forgotten his real one.
Uncle Lim liked to show off his invulnerability in front of us kids perhaps to attract more people buying his breads, or just to show that his Shen-gong was genuine. He would suddenly pull up his shirt exposing his big tummy, and then Uncle Lim would take one of his saw-like long knife he used to cut bread to cut his own tummy in a zig-zag motion.
Generally speaking, Uncle Lim's performance was successful as I could see only a few red marks on his tummy and no blood until one day...
As usual, it was just after the morning school session. Uncle Lim played his usual trick again but this time perhaps his 'ang kong' (patron god) didn't arrive on time. This time the sharp long knife produced a few long deep cut across Uncle Lim's tummy.
The wounds were so deep that his intestines were seen exposed. A few teachers who happened to came out of the school hurriedly sent Uncle Lim to the district hospital.
I have not seen Uncle Lim since the last incident. A few weeks later, I saw a young man selling bread at the usual Uncle Lim's bread stall. When I asked about Uncle Lim, the young man just said that Uncle Lim has retired from his business.
I thought Uncle Lim perhaps was too shameful of that day's incident and no face to face the kids.
Looks like Shen-gong is not fool-proof. Since we cannot be sure when it can function and when it can fail, maybe it is best just learn it and keep it to oneself for good.