heat stroke

took my dog on a short hike the other day, he has a very short snout, and i guess could be considered a bracychephalic type dog. so he got heat stroke, it was very scary, with the assistance of another strong man that happened to be hiking, we were able to carry him quickly back to my car, get him in the ac and water to him and he recovered. the guy really is a hero. i dont know if we would have made it without his help. 

this was really strange because it was not that hot out, and my dog "exercises" more than he did on this short hike no problem, and i have taken him on many much longer tougher hikes no problem. It came out of nowhere and seems almost for no reason. The only thing i can think of is that we havent gone hiking for a while now so maybe he is not in as good of shape as he used to be.

with this scary event, and the drought, and the summer coming, and me expecting it to probably a very hot summer I want to plan ahead. where i live it can be as much as 110, 115 degrees in the summer.

I have a shared yard and have to keep my dogs chained while Im at work. They have acess to shade, and a large kiddy pool for cooling off, but the summer is so hot, that the pool water gets so hot, there is no point in even going into it as the water basically gets hot.

so other then the pool and access to shade, what else can I do? im looking at maybe those ice cooling collars or jackets for them, although I dont know if these would be safe to leave on them all day while im gone at work?

any suggestions to beat the heat this summer for chained dogs would be appreciated.

ps. I am thinking of just leaving them in the house with the ac on while im gone at work but there is a danger there because due to the extreme heat, the electricity regularly goes out, and if in the house with no ac would be a death trap, they would be better off outside.