It is very easy to run over something and have it puncture but not stay in. We once had a large piece of sharp edged gravel take out a tire. We have a TPMS so we knew immediately when the tire lost air and were able to stop and look back to find the culprit - this was in a gravel parking lot. A nail in a board could do it easily. A sharp piece of metal sticking out of the ground could do it. Lots of possibilities. Nothing to stop a bad guy who really wants to from putting something both in front of and behind any given tire. TPMS is the best investment in tires you can make - less than the cost of one tire to protect them all.