There are different ways to knock out Rexes but Traps are probably the best solution. You can use three Stone Dinosaur Gateways (Rexes can't destroy stone) and a Large Bear trap by leading the Rex into the BTrap and surrounding it by Gates. Or you could also use a Raft Trap which is a better way to spend resources, since you can move it instead of remaking Traps. You can also get your knocked Rex to safety by taking advantage of the movement capability. I currently cannot think of any other ways to trap a Rex, but if this was helpful, please leave a like. ❤