Cleaning him with a brush and bathing him and shampooing should be your course of action. The obvious thing to do is get him out of there and get him cleaned. However, you should first wear gloves and approach him to keep your hands from stinking like him. Use rubber gloves with a good grip to pull your dog away from something dead.  Once he is out, brush his fur to remove debris and toxic organisms from his body before taking him to a bath and shampooing him well and for a long time. You can orange peel to the water since citrus breaks down the grease. Once the bath is over, pat him dry and hope he is clean enough to chase the smell away.