Suggestions for outdoor use of retainers
I've had fairly good luck with this sort of eyeglass retainer--make sure that the little metal rings holding the rubber earpiece connectors are fully closed--if the split ring accidently opens too much with prolonged use, the strap may slide out of ring. I replaced the rings with fully closed, wrap-around types (or the strap end openings could be tied directly to the rubber pieces with loops of sturdy thread). Out in the field one day, my eyeglass cord came loose this way while removing my glasses, but the problem can be remedied as described above if one wants to go to the trouble.  Otherwise, these retainer cords are thin, durable, and comfortable, and the end pieces are flexible and secure. After that minor repair (perhaps the company should replace the split rings with something more reliable), this kind of retainer design works very well for me. As another option, Chums makes retainers with straps directly fused to the rubber end pieces, although the cords are a little thicker, and that design is also comfortable and secure.
Rating: 4 stars