If you have a long gun for self-defense, the first thing you should mount on it is a good light. The second thing is a good sling. While my personal preference for ARs is a two-point sling like those from Viking Tactics or the Vickers Combat Applications Sling from Blue Force Gear, I think single-point slings are fine for shotguns. No matter which type you prefer, you need to think about what to do with the sling when the gun is not in your hands.
Most of you probably keep your long gun stored in a safe, closet or behind the door. Some keep one in their vehicle (most law enforcement officers have one in the trunk or in a rack). When something happens that requires you to grab the gun, the last thing you want is for the sling to get caught on something and slow your movement. This can also be a concern when you are moving or trying to take a standing shot.
A simple solution is to run a couple of heavy retainer bands (rubber bands) over the sling near the buttstock. Then "S" fold the sling loop and tuck it under the bands. This will keep the sling tight against the side of the gun. It won't interfere with the operation, but it will prevent hang ups as you pull the gun out of storage. When it is time to "sling up," simply grab the sling and pull—the S-folded excess will come out of the retainer bands and you can slip it over your head and support arm.
For single-point shotgun slings, I put the bands over the stock and tuck the sling against the stock opposite where my cheek goes, so when I get time, I can deploy the sling and slip it over my head and arm.
This only takes a second or two for either an AR or a shotgun, and it really pays dividends when you have to move and/or engage quickly as soon as you pick up the gun. It also prevents those embarrassing hang-ups on gear shifts, door knobs and all the other things out there waiting to grab loose straps and gear.