Once knocked out, you can honestly get away without taming spikes if it's just a good Rex. Nothing naturally attacks them in the wild if it's not fully tamed. You don't need to waste material and sit next to the rex if you're kibble taming it for 3 hours. Just knock it, fly back 10 mins before torpor time and make yourself productive. Unless you're on a busy server with a lot of traffic
I have figured out a new way to tame dinosaurs cut off the dinosaurs meat wise in the area try and keep the dinosaur in the area and send a dodo bird out to attack the tea Rex with bunches of Botox in and it had the tea Rex eat the Botox and it’ll knock it out you go feed it meet make sure you have plenty of Botox in and you’ll have a pet your ex and no I would not recommend trying this whenever your level one side effects may be dead dodo bird hey might find you and run but seriously You better find a good hiding spot
If you are on an animal it's way easy to tame these guys. I'd also recommend having the kibble and having a creature of any kind with high health. You can knock these guys out on foot too, but it's a lot harder and you risk other animals killing you/the rex. I'd also recommend not going after any mate boosted rex, since the torpor you do is directly related to the damage you do.