Schwalbe says the Marathon Plus is the most puncture proof tire in their lineup. Well, i had yet another flat with one today.. and i have some insight about this tire ( i've owned a few in different sizes and treads )..
What was the cause? the tire's metal rib popped out and stuck into the tube.. and this tire only had maybe 50 miles on it.
So i took the opportunity to cut the marathon plus apart to see how thick it really was. 7mm at most. 4.5mm at the edge..
The only special thing about the tire is that the blue rubber layer is ~33% more difficult to poke through than the black rubber, but if your tire is not at max PSI at every ride, it's no better than any other tire, maybe worse, because the outer 33% is very thin and not protected.
To be honest, i haven't been checking my PSI at every ride. It's been between 25-40PSI.. obviously that is not enough.
But even if you have your tire at 60psi, you are in trouble from getting poked by a goathead or metal object during a turn. Some cheap MTB tires have much thicker rubber in that area.. every time i've had a flat on a marathon plus, it was on the outside 33%.
https://www.schwalbe.com/en/tour-reader/marathon-plus-tour.html
Marathon plus tour is a little better.. slightly thicker rubber tread.. but i've still had a couple punctures on the outside.
Where i live ( Utah ), i have a lot of road debris that has spoiled bicycling for me for the last 5 years. I have tried all kinds of puncture proof tires and never found the holy grail. I think i spent more money on tires and replacement tubes than i have saved on gasoline.
If you are in my position, then motorcycle tires really are the only way forward.. no tubes / slime seem to have mixed results.