Rectal pain is a fairly common complaint. Unfortunately, because of the sensitive and often embarrassing nature, people defer seeking medical advice until the disease has progressed. I would encourage your husband to go to his primary care physician
to have this evaluated.
There are many causes of rectal pain that could be causing this. Most worrisome would be a nerve impingement -- this can happen if there is arthritis in the back or other obstructing mass that pinches the nerves that feed that area. This can eventually lead to weakness or loss of bowel / bladder function. This can be evaluated by your physician. Another possible problem is a prostatic mass or inflammation. The prostate can develop cancer which can can cause pain, or can simply be inflamed (infected) and cause pain. These can also be evaluated by your husband's physician.
Keep in mind there are external hemorrhoids which can hurt, but may not be readily visible without an anoscope (a medical device). These can cause pain if they have low blood flow.
Another common cause of pain is an infection in the area's skin. A pilonidal cyst is an infection of the hair follicles in the area. There can also be a perianal fistula which can cause pain. Anal fissures also cause pain -- but normally worse with a bowel movement.
There are many causes -- this however requires evaluation by your husband's doctor
. Because of his age, he should also have a colonoscopy
which can evaluate the area. Good luck!