Mmm, it soundsl like you've got one of the prostrate forms. Could it be this?

Iseli has this selection, which is more upright and hardy to z4. I've never seen it offered at a retail nursery.

It definitely wasn't sold as such, so if it is a such a form, it was mistakenly propagated.

The foliage smells wonderful btw.

Just looking at my https://www.mda.state.mn.us/plants-insects/cold-hardiness-list

Thuja koraiensis is rated the same zone hardiness as Thuja plicata, so unless there would be other factors involved, you might have as good of a chance as you would with Thuja p. imho.

From what I've seen so far, this list tells it like it is and doesn't exaggerate hardiness zones like some sellers tend to do.

Deer eat anything green, especially when ground is snow-covered (as you know). Doubt if one or another arb species is any different. Deer have practically denuded all my hollies here after the last snow.

I'll have to agree ben.

Deer won't starve themselves to death during a harsh winter.

Out at my old place in the country, a deer would spend the harsh part of the winter under a jack pine that had low hanging branches and would eat the needles off the branches to survive. Normally, deer would not consider eating mature pine needles but it's the will to live.

To add, neighbor of brother in PA had green giants (T plicata x T standishii) planted along driveway, and these were stripped bare up to the deers' reach first winter. So different species of arbs aren't going to matter.

"Thuja koraiensis is rated the same zone hardiness as Thuja plicata, so unless there would be other factors involved, you might have as good of a chance as you would with Thuja p. imho."

Maybe, but it could also be that Korean arborvitae has simply not been trialed to any significant degree in the upper midwest. Iseli has Thuja koraiensis 'Glauca' listed as z4, which could be warranted or simply marketing illusion. As an example, Korean Fir (Abies koreana) is often listed as z5/6 on various internet sites, but has proven (at least to me) to be hardy in z4 west-central Wisconsin. It seems that any plant coming off the Korean peninsula, Manchuria, and the Amur river basin is worth a try where I'm at.

" Deer eat anything green, especially when ground is snow-covered (as you know)."

I won't argue with that, but they definitely have preferences. This is especially true in a suburban setting where there is a botanical smorgasboard for them to choose from. There are no starving deer in this neighborhood, even during difficult winters.

' it could also be that Korean arborvitae has simply not been trialed to any significant degree in the upper midwest '

That could very well be but the list I posted comes from trials at the U of MN so for my area, it tends to be more accurate than most.

And when it comes to deer, you need some sort of deterrent otherwise deer will eat accordingly, to what they like the most first and then go down the list and be less fussy the harsher or snowier the winter gets. :-)