I backed my trailer into the usual spot on one particular commercial job site. Then I heard the sound of rushing air as the tire on my trailer went flat. There were broken bottles all over the pavement. I plugged the tire and pumped it up. I used the backpack blower to clear the glass off of the parking lot. Over the next two days, the same two trailer tires went flat 7 times. Some of the tire plugs leaked, and some new leaks appeared. I'm thinking that maybe some glass was inbedded in the tires and just worked its way through the tread. Anyway, both tires have been replaced. I used to put Slime in my tires, but haven't done this for a couple of years. Maybe its time to be more pro-active.