Spar work

I've had more hands with AFSs than Cincinnati anchors.
"Polishing" the bark by running it back and forth at the angle it will get pulled may help.

A horizontal circle is easy to choke tight when up in the spar.
An angle oval of rope at the choke releases easier, yet is still secure, if the bark has some friction to it. Eucalyptus and madrone are slick.