Yes, you can make sunglasses with duct tape to make them be durable. You could just make the duct tape to stick at the frame's slit place. I think you'd better let the client at the eyeglasses store to help you do this. It could make the sunglasses look durable which could be worn for many years.
Yes, nowadays some people just DIY their sunglasses with duct tape so as to look personalized and fashionable as well as preventing too much light coming into their eyes. First of all, you can pull out some duct tape, tape four strips together and then secure them so as to allow only a small slit of light coming in. Another option is just to tape the duct tape to itself instead of sticking the glue directly on your glasses. After doing this, use some duct tape strips to hold it to the top and bottom edges of the lenses. Then a simple duct tape sunglasses are made. If you would like to get to know more information on making duct tape sunglasses, you can refer to the following web site.