I was searching for high lvl rexes on lava island and found a 145 carch on lesser one instead. I instantly decided to tame him and spend like 1,5 total. A lot of time he was doing stupid things but now I understand how to tame it, how I did it in the end:

Crafted like 4 stone gates, placed 3 in the form of half circle

Agroed him and made him attack gates

While he was busy locked him

Went away to rerender, it will make him stop attacking gates

Lure a rex and kill it

Grab his body and offer him

If he doesn't sniffing or eating rerender again

After he eat it freed him

Commite massacre killing rexes, carnos and argies

We are friends now, he is awesome:)