I do the open windows at 3 AM, close windows by 8AM thing to try to keep the house cool. Opening windows before 3am is useless here, as temps stay warm into the night. And since the windows are open, I have to stay up to make sure that my 'security system'

isn't triggered by outside noises, disturbing the neighbors.
(Look on meteocentrale.ch to see the temp prognosis throughout the day to determine when the low point in your area is expected. In my area, low temp of the day is usually 5 AM, high temp 5pm.)
Keeping the house dark during the day helps - all blinds are shuttered by 8am. A bit depressing for the humans, but it really does help keep the house cool.
Walks at 5AM, back by 7:30, bring plenty of water along.
(FYI, best not to let your dog drink from a run-off stream running through a farm field; chances are that the water contains fertilizer. And beware any water recepticle where you don't know the property owner - lacing pet-friendly water buckets with anti-freeze is a favorite tactic among the dog-hating crowd. Only drink from fountains labeled 'Trinkwasser', using your own container if your dog isn't trained to drink straight from a fountain.)
I always have towels in my walking pack - should a dog show signs of fatigue, I soak a towel in water, drape the dogs, rest for a minute. (Any signs of heat exhaustion, call the emergency vet immediately!)
Sadly, dogs have been banned from the trails along the creek in our area - that was a great shaded walk, with plenty of opportunity to dip in the creek to cool off if needed.
At home:
Frozen 'tuna-cicles', ice cubes with a bit of tuna in them, are a favorite cool-down treat.
Also, I take a big tub-like bowl and fill with cold water and ice cubes, kongs, toys, chewsticks - and let the dogs play 'bob for treats'. A good cool down game. Add a clicker, and do some 'pick up the thing I name' training.
Apparently shelties melt in water

, so the hose/sprinkler is a last resort.
Fans at floor level help, most of the dogs camp out around the fans - but my Belltie doesn't like drafts, and will take himself off in a huff. (He is Swiss, btw.

)
But if we are in for a protracted heatwave, nothing works to cool the house down once the nights stay above 18-20 degrees. 2003 was such a year, so I broke down and bought a portable air conditioner - installed in the dogs' room of course.

. This gets turned on maybe 2-3 weeks a year, some years it's not needed. But as I have rough collies and shelties - long-haired, double coated - several of whom are elderly dogs with dodgy tickers, I can't risk heat exhaustion with them.
Hope it won't be a scorcher this year...