How and what to do about it?
It has happened to me 3 times in the last two years. It seems like something is on the tire, and it gets worse over a few minutes. I get off to look and the tire liner and tube are bulging though the outer tread of the tire. While I watch, the bulge is expanding. The whole area around the hole begins to bulge balloon-like. Except that I use Stop/2 tire liners and the thick puncture-resistant tubes, the tube would have obviously blown.
Nothing notable happened in the, say, half hour before the events. In fact, in two cases I was in some store for the previous hour, and everything was fine for the first few minutes of the ride.
Examining the inside of the tire, the visible cords are frayed. The other cords that run in the opposite direction, crosswise, seem intact. The tube pressure just ripped through the outside rubber by pushing those cords out of the way.
I don't inflate the tires beyond the recommended max. The tread is not very worn. In one case, the tread looked virtually new.
It is hard walking a bike and groceries home for like two hours. A flat could have been fixed. After this happens, the tire is absolutely shot because of all the broken cords.
Just so you'll know where I'm coming from, I don't ride the bike for fun (although I have come to enjoy it), speed, or athleticism, but for utility, so I'm not concerned about the weight of tires, tubes, liners, etc.
The tires have lasted roughly: 1.5 years and 7 months on the back; and 2.5 years on the front. In no case have I had a flat in this time frame.