Y'see, kancho is mostly an elementary school thing. I'm grateful to say, kids grow out of the "Hey! Wouldn't it be fun to stick my fingers up someone's butt?" phase somewhere around 12-13 years old. So it's rare to get any kancho attempts from the ninensei or sannensei. The ichinensei on the other hand...while they're not particularly prone to it, they might bust it out for special occasions (like "welcoming" the new foreign teacher). April is particularly dangerous, because that's when the ichinensei enter jr. high school straight from elementary school. New school, new asses, it's like unlocking hidden levels in Ass Raider or something.
I hadn't had any attempts since last April. The ichinensei had just entered jr. high, and one day one boy tempted fate against me. Thanks to my trusty Kancho Sense™ I avoided getting my oil checked, but I realized that if I didn't head this shit off at the pass, I'd have to be parrying them for at least the next few months. So I turned around and chased the boy down. He was surprised, he probably didn't think I could move that fast. I caught him...I restrained him with my left hand, dropped to one knee, put my right hand back as far as I could, said "One thousand years of pain!!" in the over-blown anime style and everything, and prepared to kancho him straight to Hell. The boy was freaked out. I think tears were even streaming down his face. I don't blame him. In retrospect, I can't even imagine - you're a 12 year old Japanese boy being forcibly restrained by a large black man who is bound and determined to penetrate your ass. I would have been crying too.