What worked well for all our garden fences, made of chickenwire over cattle panels, with a gate of the same, is a bungee cord. Hook one end to the gate and the other to a wall of the enclosure, and the gate stays firmly closed. When I'm inside it's not tightly fastened, but I don't think rabbits and such are getting in when I'm in there working; they get in when I walk away without latching it, just to go to the house for a tool or sunglasses or whatever, and then get distracted and forget I left the gate partly open...Mostly I can latch and unlatch with one hand, except for one garden that takes a firm stretch of the bungee cord which I find takes two hands.
Gotta mention--my husband once got locked in the chicken coop, just as someone mentioned here, and was wondering whether he'd have to try to escape through the chicken door, which would likely require shedding all his clothes, by the time I heard him yelling and let him out. I then had an image in my mind of him crawling through that hatch and down the ramp naked, and I gotta admit, I was thinking what a lovely video clip that would make...