I put an Alolan Exeggutor in a gym at the botanical gardens I hiked on Sunday. It’s still there. No one has attacked the gym in 3 days – it would have fallen easily – and someone golden raspberried the whole team of defenders before closing time today!
My guess is most of their weekday visitors (it’s only open 10-5) aren’t in the Pokemon Go demographic. Now I’m wondering if it will make it until Saturday morning!