Trees and horses

[RQuestarabians@aol.com]

Would anyone be able to recommend what to plant alongside my arena for 
privacy. Is there such a thing as a bush or tree that is not poisonous to 
horses yet they will not eat (destroy) it when they are turned out? I live in 
hot sunny dry California. Does anyone have any suggestions?
Thank you.
Robyn Levash & Classy De Washoe & Wiley Coyote
( Gee mom those pine trees you last planted were hoof lickin' good! )