The best way for me to knock these guys out is to place down stone pillars in a line but spaced out to where you can easily squeeze through but too small for the rhino. Then lure it to the pillars and run between them. The rhino will get stuck on it and if you're lucky, it'll be aggro'ed on the pillars and not you. From there you can start tranqing it and if it goes around the pillar line just go through the gaps and continue tranqing. Dont get too close though cause they can still hit you through the pillars. Keep tranqing until its knocked out or runs away from low torpor. If it gets unstuck from the pillars and runs away, chase it and keep tranqing if it turns around to try and kill you just lure it back to the pillars. This method does require timing, positioning, and being cautious.