My experience with GC R1(ag) tires. Knew from the start that there was too much scrap in the 150yr old farm I'm living in to cause punctures. Had the fronts filled foam filled at an industrial tire shop when new. Added about 40lbs ballast to the front. I do not drive on pavement, after 18 years, 900 hours, tire wear is still proportionate to the unfilled rears.
Foam filling the rears would have made the ride too hard on the back/kidneys, and really didn't require it, so no rim guard. I have found that if the tire pressure is too low (even liquid filled) that the rubber tire will spin on the rim if trying to use as a bulldozer. Breaks the bead and goes flat, or won't move at all. I would suspect the rear punctures are from trying to force the bucket into a pile of stone instead of scooping it off. I've had rear flats, but never from punctures. Bead brakes, weather checking and valve leakage.
If you stay with the turfs, keep an eye on the tire pressure, and possibly invest in chains for them if doing any wet dirt work.