Yes, they work, but I prefer using entanglement instead of a sliding lock. Essentially make the same setup with a crossbar or X welded near the bottom. When they dive, they wrap, and the snare gets shorter and shorter. With a sliding lock, you must use a very short snare and still need to have a neck catch if the water is less than 5 feet in my opinion to ensure there won’t be any problems. Beavers are long, strong, and a cinched snare becomes longer. If they can get their nose to the surface, you’re going to have a problem on your hands, because now you’re trying to dispatch something that can go under several feet of water.
HOWEVER, when this type of setup or entanglement setup works the way it’s supposed to, it’s great.