He didn't keep the whole two inches. His starting size was 4"x4", after a few months (this was years ago, so I don't remember exactly how many months, but it was really quick) he peaked at 6" x6". Having reached his goal, he lost interest. After ceasing the exercises, there was some diminishment, and our most recent measurement was 5.5"x 5.5". He started maybe five years ago? I'm not sure. He only did it a short while. I was completely opposed to it at first, but he was having fun doing it, and the results made him feel better. Before the growth, he refused to have any kind of sexual contact with me. He would let me see his penis, and he would masturbate and I could watch, but he wouldn't let me touch it. Afterward, he was a lot more fun.
Every once in a while, he lets me stretch it before he goes to bed at night, just for a minute or so. Then he flexes his PC muscles, and we just watch his cock fill up. He will keep it flexed as long as he can, on and off for 5 or 6 minutes, and when he does that, it looks gigantic to me. Much bigger than usual. I have never measured it at one of these times (we are usually going to sleep) but I'd estimate it to be 5.75" x6", which to my eye looks very different from his normal size.