As much as i hate making a tip for this demon, put 3 dino gates down in a triangle and close them all. Put the troodon inside with a flyer or lead it in. Get a parge dinos about rex size. Maybe 2. Put it on neutral. Tranq it. Once tranqed use a tanky dino such as a carbonemys and stand near the rex. Release the troodon and let it attack your turtle while the rex slowly dies. If possible place 2 rexs asleep together to kill both at the same time.