You know the tubes that come pre-filled with slime will seal any puncture or pinch flat up to 1/8 of an inch. I know that a few guys here on the forum have run over major debris like roofing nails and drywall screws, and slime isn't going to do much good against that. But in 3 years, I've only had a few flats, and none of them were from running over anything. One was caused by the sidewall on my rear tire wearing through, which happens after almost two years (it was a great tire, the specialized hardrock'r, got it for 1/3 of the original price and it lasted a very long time until that sidewall gave out). Another was caused by over-inflating with a pinch flat, and another was caused by improper tire installation when I installed a new tire (the one that replaced the specialized tire, in fact). Here is the thing. Slime tubes won't prevent all flats, but it will drastically reduce the occurrence of them, and its easier and cheaper than going tubeless. I get that the tubeless valves are only $16 apiece, but you still have to buy stronger tires and you also have to seal your rim. Slime tubes are $9 apiece, and no other modifications are necessary. Like I said, only 3 flats in 3 years with slime tubes for me. Just giving you another option to consider here.