sores on back that smell

It sounds like he has bed sores/ pressure sores. They usually occur in people that are confined to wheelchairs or who are confined to bed for a long period of time. However, it is possible for ambulatory, seemingly healthy people to get them as well.
Avoiding sleeping on his back would help a lot. Also, using a mattress pad, memory foam or air mattress would help to prevent them. He should also have a doctor dress the wounds.