A "guy" cannot do anything to make sex last longer for "his woman." Possibly he can learn to make sex last longer for him. Do a google search on premature ejaculation.

Cock rings do not make sex last longer, they are intended to keep you firmer and may actually cause quicker response.

Medically, I recommend you stay away from messing with cock rings unless a doctor recommends them to you. They work by restricting blood flow with the intent of keeping blood in the penis. It does not take long for this reduced circulation to cause other problems. I remember as an intern in an emergency room cutting one off. What relief he must have felt! They are not toys even though they are sold as such.

Please read the following thread:
http://www.sexinfo101.com/forum/new_...e_problem.html

...including my second and third reply.

In addition, please go to the link mentioned in the second post:
http://www.sexinfo101.com/forum/new_...re+Ejaculation

You will learn about the condition known as "Premature Ejaculation" that affects most teens and guys up to about their mid-twenties. In addition, I describe a training exercise that you and your partner can do to control the tendency to climax too quickly.

If you have any questions or concerns after reading the information in the two threads, feel free to ask.