We'vee found that what deer leave alone also holds true for gophers. Here is our deer resistant plant list.Â
https://sloatgardens.com/wp-content/uploads/2014/03/Deer-Resistant-Plants.pdf
Our picks for the steep slope in full sun are: Rosemary, Lavender, Euphorbia, Oregano/Marjoram, Salvia (including culinary), Thyme, Coleonema (breath of heaven), Grevillea, and Correa.
As far as resistant trees, most fruit trees would require protection when young with some type of fencing around them. Persimmon, Olive, Pineapple guava (Feijoa), and Fig are kinds that are considered the most deer resistant. Older citrus is usually left alone but young plants are fair game, especially when other browse plants are not available.