That photo I posted was the older Marathons sold up until maybe 8 or so years ago. I did not flat on that trip, but when I saw the thorns I stopped and pulled every thorn out of my tires, took several minutes. I then picked up the bike and carried it back to the pavement instead of rolling it on the ground from where I had pitched my tent.

Can't say if they are prone to flats or not, I might have just been lucky. I used a disposable plastic sheet under my tent, that accumulated a lot of thorns.

A year and a half ago I got my first flat in one of the newer Marathons (with Greenguard), but I had picked up a construciton staple that would have flatted just about anything with the possible exception of a Marathon Plus.