quoth rekmeyata:

'I never saw the need for two tire liners'

The Slimes alone weren't working. When I shopped the StopsFlats2s
looked like the best choice. I saw no reason not to use both; I hoped
they would move a little bit between themselves and cut goathead
thorns or, at least, tilt them away from going directly through to the
tube. I saw no kevlar liners so I didn't look hard enough. I'll keep
them in mind.

'Living in high vs low ozone, not sure what you mean, I use to live in
Los Angeles area back in the 70's and 80's when pollution levels were
a lot higher then today and still didn't have issues with tires
cracking before they wore out, even stored tires didn't crack. I have
had or seen cheap Walmart type of tires crack fast but not decent
tires at least not over a 6 year period that I had tires sitting on
one bike I rarely used.'

It's no secret that ozone attacks rubber. It was the subject of my
Father's master's thesis in 1947. Perhaps rubber makers have found an
ozone-resistant formula.

Quoth Al1943:

'We have a LOT of goatheads in this area. I find that most
goatheads are picked up in parking lots, rest areas, and on
paved trails where newly cut grass has been blown onto the
trail. In my opinion the best way for a road bike rider to
avoid goathead flats is to avoid goatheads. I never ride or
roll my bicycle across grass or through weeds.'

I'm out to have fun, which means not staring at the pavement the whole
time and traveling through drainage ditches and catchment basins and
dirt trails in the foothills... The goathead-freeest places are
well-traveled roads: car tires pick them all up - but that's no fun.

I also use the extra-thick Sunlite 'thorn-proof' tubes. Not sure they
help.