Dogs in the Yard
If the dog must be kept in the yard during the hot parts of the day in the summer it is absolutely essential that there be a dark, shady place where the dog can escape from the blazing sun. Make sure there is a good source of ventilation (moving air). A tree may not be good enough. A ventilated dog house, or a pen with shade cover, or a covered patio is a must. Make sure that there is adequate shade at all times of the day that the dog is outside.
Dogs and Water
If the dog is outside, make certain that there is a good supply of clean water in a weighted dish (or two in different locations in case one gets knocked over anyway).
Dehydration can occur with dogs just like with humans. Your dog gets rid of heat through panting, or through the pads of its feet. Also - if you leave water in a bowl, consider a spill proof bowl.
Keeping Dogs Cool
Some dogs enjoy water and can keep cool if a misting system is left on during the day, or if there's a kiddy wading pool for them with a couple of inches of water in it where they can sit to cool off. Keep these in the shade, too. Sitting in a tub of 110 degree water won't help the dog. Some people I know say that they provide a sandbox with damp sand for the dog. Digging must be allowed in the sandbox--you'll only frustrate a dog with a sandbox where digging is not permitted!
Avoid exercise in the warmest part of the day. Early morning or evenings are the best time. Limit the time according to the temperature.
Never leave a dog in a parked car. The temperatures can reach over 150 F (66 C). Heat stroke, or death can result. It is a common error to believe that leaving a window partly open will eliminate problems with heat.
Other travel may require special precautions. If flying, make sure your flight is direct. Dogs have been injured by being held in baggage compartments on hot runways (sometimes with ventilation cut off while the plane is parked).
If traveling in a car, make sure you are prepared with ample water (and an occasional break for potty and exercise). Watch out for your dog's safety, allowing them to stick their head out the window (wind, dust and particles blowing in their face) can result in eye or nose damage or even swallowing something that may block their windpipe. Also, remember that your dog can get injured in car accidents just like a human. Most experts suggest having them ride in a crate or using a dog body harness. Never let them ride in the open back area of a truck
If you leave your pet at home, make sure someone is there to supervise him and provide him with his needs. Consider using day pet care, or boarding kennel for longer trips. Outside might not be a good idea if left alone - not only is hot weather a concern, but also summer storms can be dangerous or cause anxiety.
If you suspect heat stroke, you should seek veterinary assistance immediately. But you should first cool the dog by using cold water, either with towels soaked in cool (not cold) water, using a hose, or even a cool bath. Make sure there is plenty of ventilation. Ice packs or cool towels can be applied to the dogs chest, neck and head areas (only). you can give them sips of cool water or a few licks on ice cubes. A trip to the vet could save your dog's life.
Avoid walking or leaving your dog on hot surfaces such as sidewalks, asphalt or sand. These surfaces get very hot and can burn the paws.
Not all dogs are swimmers - make sure you supervise your dog if near a lake. Also remember that your dog may drink dirty water and become ill from parasites or other undesirable contaminants. Drinking sea water (salt water) can be deadly in quantity. Some lakes and most pools are treated with chemicals - this is not a good place to get a quick drink.
Dogs in the Pool
If your dog has access to your swimming pool or spa, make sure the dog is trained to get out of the pool. The dog needs to know how to get to the steps. If there are no steps or shallow areas, like in some lap pools, make sure the pool is fenced and locked so the dog can't get in. Every year puppies and dogs drown in backyard pools because they could jump in, but they couldn't get out.
Dogs can get sunburn just like humans. Use sunscreen, There are products available for dogs, but a good hypoallergenic product can be used on noses and other exposed areas. You may also wish to consider products for the coat which protect from harmful UV exposure (and they will prevent damage to the coat as well).
Summer is the season for insects. Protect against fleas, ticks and heartworm. Consult your veterinarian for recommendations in your area.
Warm weather also brings on allergies from pollen, grass weeds and fleas, etc. If your dog is chewing on himself, consult with a veterinarian.
Careful of what dogs might drink - antifreeze can poison your dog and a little puddle might be tempting to drink (it tastes sweet and seems to attract dogs)
Use common sense.