Trouble with sex

An elderly couple went to a doctor. They told the him "We're having some trouble with our sex life. Could you watch and give us some suggestions?"
The doctor replied, "I'm not a sex therapist. You should find some other doctor."
The couple said, "No, No, we trust you."
After watching them make love, the doctor said, "You guys don't seem to be having any problems. I wish my sex life was as good. I do not have any suggestions."
But the couple came back next week and also the third week. After they had finished on the third week, the doctor said, "You aren't having any trouble for sure."
The man replied, "No, actually the problem is that if we have sex at my house, my wife will catch us. If we have sex at her house, her husband will catch us. The motel charges us $75 per hour, and we can't afford that. You only charge $50, and my Medicare pays half of that!"