Dang slime did that to my pump... Gave up the slime and bought a new pump.. I think you find also that with time the slime plugging todays holes will harden and work loose and the tube will start leaking again until it replugs itself... Not the best solution IMHO..
We have the same thorn problem here... The tires are like magnets to them... They call them "goathead" thorns around here cause that is what they look like... I can't speak to Marathon's as I have never had them but I can say in 1500 miles now I have never had another flat with the Armidillos... I still pick up the thorns and listen to them click on the road as the wheel turns but have yet to have one pucturetire... I am a happy rider again...