The Unbelievable Endurance of Schwalbe Marathon Plus Tires
I just reached 25,000 km on one of these tires, all of it rear wheel loaded touring use. The puncture protection belt is peeking through, but only in sections and not yet along the entire circumference. I'm guessing it will last till 30,000 km.
These tires are heavy as hell, so you'd better make sure you don't mind because once you buy it you're going to be riding it for the rest of your life.
And they're not immune to punctures. I've had a handful of flats on this tire, all from metal wires.
How long has your Schwalbe Marathon tire lasted?