If Memphis is as hot as it is here in Louisville, you may want to shut that dog door, and either get home at lunch to let him out, or have a neighbor let him out. We saw 2 dogs with terrible heatstroke yesterday at the clinic- and had to send them on to the emergency hospital because they were older and in really bad shape. Heatstroke can come on really fast, epecially in old, sick dogs, and I wouldn't let him make the decisions when to go out and come in today. You wouldn't want him to be overcome when you are not there.
If it is too hot outside for people, it is too hot for dogs.
If it is too hot outside for people, it is too hot for dogs.