@wildwood
Good point. Springy fences guve way but don't adopt any permanent bend or fatigue fracturing. Elephants are about 10 tons and can knock a tree down so you'd think fence posts would be vulnerable but I've seen nature reserves, on film, where a glorified chickenwire fence (about 1.5 times elephant height) is enough to at least make them give up trying, if not stop a determined, angry, one.
I thought about electrified fencing and, seeing how flimsy it looks, have always wondered if cattle feel it through their thick hide or if it is meant for stinging wet noses?
In fiction, Jurassic Park used electric fences but lizard skin is bone dry, possibly insulating and dino skin, you'd imagine would have scales too thick to conduct the shock. Only when the scales are stretched widely apart does the skin get exposed.
Artistic licence means the author can simply say it works and the reader accepts it. Generally. ;-)