Can't cooling them down too fast cause it also?
Looking at George cross-eyed will make him founder.
Seriously, there are lots of reasons for founder to happen; horse drinking too much cold water when he's hot and sweaty, green grass, feed overload, road founder, the list goes on and on. Ponies are definitely the most suseptable but horses with a cresty neck are also big culprits.
Hair, it sure couldn't hurt anything to get them off the grass for a few hours a day. Yes, when they are fixing to founder their feet will be warm but George's are always warm so it's hard for me to tell if they are warmer than usual.