Our dilemma here is mesquite thorns on the ranch. We have a number of wheeled vehicles on the ranch so I have had the opportunity to try many approaches to the problem over the year. Interstingly enough we have never had an issue with flat tires on our tractors (Ag Tires) other then having a mesquite stump once punching a 2" hole in a rear tire (old tires; had to replace the tires). Anyway, on all of the rest of offroad stuff (Kubota side by side; 3 ATV's-Polaris/Kawasaki) and a Bobcat we have had numerous oportunities to try out solutions. Meanwhile we do nothing special for leaks in the tractor tires (which we haven't had any other than the one I described). Perhaps it has to do with the areas we use the tractors in on the ranch vs. the other vehicles.
We got the Bobcat S-650 new in 2011 and had the tires foam filled by the dealer before it was delivered. Harsh ride but never an issue with flats. Replaced the wornout tires at about 1000 hours (we also are on very rocky soil) and currently have about 600 hours on the new set. Running with Bobcat Extreme Duty tires foam filled. Interestingly enough a few months ago I was at the Bobcat dealer and noticed all of the new wheels sitting in their yard with new tires on them. Service manager told me that it was cheaper to replace the whole tire and wheel when foam filled rather than trying to scrape off the old foam upon tire replacement. As a sidebar, I also talked to them about replacing my S-650 with a tracked equivalent; he said they still sell many more wheeled versions in this area compared to elsewhere in the country due to the rocky soil. The tracked versions seem to get their tracks torn up or torn off rapidly while working in the limestone hills. I will stick with the foam filled tires for now.
Regarding ATV's and side by sides. Of course they run low pressure tires. We have been running with Slime for years. Mixed results. Most of the thorn holes plug off with the Slime but it still takes the ocasional plug to repair a larger hole. Some of my tires have 15-20 plugs in them before they are replaced due to age and wear. Last year I got the bright idea to replace the Slime with the Flatout kevlar stuff. Of course you can't mix it with Slime so it involves dismounting the tire from the rim, washing out the rim and tire and remounting the tire and adding the 'stuff'. I spent 1-2 hours trying to get the first tire off the rim (unsuccessfully) and went to our small town's repair shop that had better equipment. The owner said he would do all of the tire dismounting, cleanout, remount and add the kevlar stuff for $15/wheel (I brought the wheels in 4 at a time already taken off the vehicles). Hard to pass on that deal.
So we have been running the Flatout stuff now about a year in 16 wheels. Results are mixed. The Flatout stuff doesn't appear to stay liquid in the tire like the slime; instead it seems to coat the tire (and rim) with a gooey mess. So depending on the size of the hole you may or may not get it sealed off. Bottom line for us is that we are still manually plugging some holes, other holes are sealing (similar to the experince we had with Slime). I'm not convinced that the Flatout type material is that much better than slime or equivalent and certainly is costlier. If I had to do it over I would have probably stuck with Slime. But YMMV.
One other thing to be aware of. One time I had to replace a tire on the UTV due to sidewall damage. Had to replace the rim. Took it to the local shop. Got it back and then had a slow leak for a long time.Went back to the shop. Turns out when they mounted the new tire they did not clean off the fiber from the Slime off the rim and I was leaking from a failed seal along the rim. CLEAN the rim where the bead sits!
Finally someone mentioned that valve stems and cores can be an issue. I second that thought. Over the years we have our share of the same problem. Cheap to replace and they do go bad over time. Consider steel stems instead of rubber in the future.