On my commute to work there is no suitable public transport, so if I didn't have the ability to repair a puncture at the roadside it would be a long walk home, which is what nearly happened one evening when I got a puncture a couple of miles from work so decided to walk the rest of the way and fix it at work. This I did and in the evening went home as normal and two miles later the tyre went down again. Walked to a suitable spot near a house with an outside light (so I could see what I was doing) and replaced the tube again. A mile down the road it went down again, yes it was a buried flint that I couldn't feel with my fingers that had now pierced my last tube. Still five miles from home I had no option but to walk, which is not ideal on a very dark country lane. After half a mile or so an estate car came past me then pulled in front of me and stopped. The driver asked if I was ok and I explained the problem. He very kindly offered to give me a lift home which I accepted gratefully. It turned out he was a keen cyclist himself. When I got home I found the flint in my tyre and managed to get it out with the help of some pliers, it was very well embedded in and difficult to remove. It had only just barely managed to penetrate the Marathon Plus smartguard layer, which is why I couldn't feel it previously.