I use a 642 as my primary kayak and fishing gun; it was also carried when canoeing until my canoe got damaged and I haven't bothered to repair it (damaged gunwale and seat from a tree limb). Anyways, on the water it usually gets stuck in a Ziploc and either stuck in my pfd pocket (which has Velcro and a Fastex buckle) or secured in my deck bag or a buttpack (usually worn, especially in cold weather, sometimes just clipped to the seat). It does not have a lanyard on it; I tried a couple of options but didn't care for them. A loop of bank line with a blood knot under the grips was cheap and easy way to connect a heavy duty zinger or lanyard. Not a fan of the telephone cord style lanyards as they get hung up on stuff, especially when you're in a swamp. I started with a 686 as a boat/swamp gun and it wears a set of Hogue Mongrips with their lanyard stud that replaces the screw in the bottom of the grip; needless to say it was heavier. It was supplanted by a G27 since I actually like the 686 and didn't care about a Glock; I didn't care about the Glock enough that I sold it after I quit the job where I was primarily using it.
The guns all got wet on more than one occasion, both fresh and salt water and I would just pull the grips, rinse with clean fresh water, blast them out with WD-40, sling the excess out and wipe them down. Good to go until I could do a more thorough cleaning. They're still rust free today. Rinse your ammo with fresh water and dry but don't oil; never had any issues even after being submerged for a few minutes but I always used factory ammo. One of my co-workers used to put a drop of clean nail polish on the primers and the case mouth of his rounds. Most of the time I load the 1st chamber with a CCI shotshell and the other four with whatever I feel appropriate. I've killed more snakes with boat paddles, bush axes, range poles, etc. than I've shot. When fishing from a power boat, especially at night when we'll be coming back to a boat landing, I usually carry something with a few more rounds (usually a G26; I still don't like Glocks
).