I used to catch water moccasins back when I lived in Florida. What I would do is find them when they would be crossing this wide dirt road alongside a canal, either in the morning, dusk, or after dark, and I'd slide a stick under them, lift up, and then grab them by the tail, keeping the head-end on the ground. They're too heavy-set to strike upwards high enough to reach my hand. Small ones could be much more difficult. They're nowhere near as aggressive as people think, in fact they are much less aggressive and prone to striking than nonvenomous water snakes, particularly the brown watersnake.
Up here in Missouri, I've caught one water moccasin, and I'd say fifteen or twenty copperheads. Copperheads have a pretty good disposition, but the rule still applies: smaller venomous snakes are trickier to handle.
