I have never seen rat or deer issue's with Kei apple. There are 2 huge bushes at UCSC right in constant every day sort of deer grazing and bedding habitat. Coincidentally there is a huge wood rat nest in one of the 2 bushes, and a gaggle of Quail.
Maybe they have better options than Kei Apple to eat here , whereas it is considered primo food in your location.
Rats can get a taste for different things and then girdle , or they do it at the end of summer when there is no water , just for the moisture.
I was very surprised to see rats girdle Cherimoya, since nothing including gophers seem to touch them.