what kind of temps are you talking? 80's, 90's, 100? is the dog an outside dog or inside? a couple of pretty important factors.
shade, shade, shade is very important! you can build an elevated platform off the ground just 1' that will allow air to circulate up under the dog and all around it. this helps quite a bit. also, if you have any natural type breezeway (or off the corner of a house, etc.) make accomodations there. plenty of water, refresh it everyday. you may even get a kiddy pool or something for them to swim/splash in. make sure to replace the water regularly, don't let it get stagnant. if it's an indoor dog, acclimate the dog to outside temps slowly by putting them out early in the day and allowing them to adjust as the heat goes up. don't take them from 70 degree house and put them in 95 degree heat. at the very least, section the dog off an area of yard that you don't care if he digs in. dogs dig to keep cool.
i have seen people build a dog house and put an ac unit in it. you'd be surprised how cheap you can find an old window unit and incorporate it into a dog house if you look hard enough. they aren't that expensive to run either. hth!