Leave a radio or TV on. The sound of human voices is very soothing to a dog. You can hook up an appliance timer to the TV or radio if you don't want them running on all day. You can hang items from trees or other structures in the yard, such as a tire or a toy or a nylabone. If you use a doghouse to give your dog shade during the day, attach a ramp to the house so that your dog can climb on top and hang out there.
Dogs love to lay about on high.
You can also make him a platform by attaching a flat wood board to a crate, or by providing him with an old wooden or plastic table. Make sure however that your high resting spots are nowhere near a fence so that your dog can use them to escape from the yard. If you have a dog who enjoys ripping up pillows or stuffed toys, a great exercise for him involves a wooden or heavy plastic crate with a four or five inch square opening. Put some good-smelling treats in the crate and then stuff it with old rags or towels that you don't mind having ripped up. The dog will enjoy pulling the stuffing out of the crate to find his treats.