What he doesn't eat, he lines up on the porch. I know he's had a mouse when I find the stomach on the porch, almost every night lately. That's the only part he won't eat. He doesn't eat the squirrels, chipmonks or moles that he kills. Just leaves them for me.
For a month or so this summer, he started bringing me live mice to kill myself
That didn't last long, thankfully! I rarely find cat poop in the garden areas. We (cat and I) frequent that area enough and his cat nip grows there that he eats, so I guess he is not inclined to poop there. He uses the wild area for that, I assume. He buries it anyway, so if he is pooping in the garden, I don't know about it, which suits me.
They are both very healthy, disease free cats and the country field mice he eats are not prone to the diseases and worms that city garbage mice have.
Outdoor cats in the city are a completely different thing.