Molbak's has an assortment of hedging plants on display in the northeast corner of the outdoor nursery yard.

New plantings need to be protected from animals.

We planted Leylandi Cypress last fall. They even grew during the winter and have established themselves very well. I know they need pruning and shearing but after researching everything I thought them best for our situation. No. 1 reason - deer don't eat them.

Has anybody tried pacific wax murtle for this purpose?

There are many plantings of it around, including those used as hedging and screens. Prone to weevils if beneath taller evergreens. Prone to deformed (lanky) growth if shaded much.

Lynwood CostCo has it sheared into tight shapes, as is so often the case with shrubs in commercial landscaping these days. Seems to be taking this quite well, probably has ability to grow back from tip damage due to outer coastal native habitat.

I've used the pacific wax myrtle as hedging, on Alderwood soils too. You're pushing its limits if you want it at least 12ft tall. And when you say this area has great drainage, and it's already on Alderwood - how to say this - you're going to have a drought problem there. Alderwood soil is officially classified as 'excessively well drained'. Plan on watering any new plantings for a few years to get them established.

A couple of dense evergreens that would get the size you want are holly and Portuguese laurel, but both will produce berries that the birds will spread all over the neighborhood. I have a totally-volunteer screen between my house and the apartments on the next block, and the primary evergreen screening comes from holly, cotoneaster and young madrones.

The arborvitaes Pyramidalis and Emerald Green make excellent hedges, but deer do eat them where they can reach, giving them a lollipop appearance, and they need to be planted close together because they're narrow and slow. If you lined the hedge with deer mesh you could avoid that lollipop look, and the mesh would not be obtrusive against the foliage. Leyland cypress grow very fast, but also very wide. Italian cypress are narrow like the arborvitae, but much faster growing, and can reach 12ft in a few years. Dunno if the deer would browse them.

Arbutus unedo, a madrone relative, is a very attractive evergreen that can be used as an informal hedge, but I'm not sure about it getting to 12ft tall. Most of what you see in nurseries is Compacta, which won't get that big. I have gotten frost damage on it in very bad winters, but it always grew out of it in spring. Ceanothus 'Victoria' could potentially get that big I think, most of what you see out there is pruned much shorter. Again it can be damaged in bad winters, but it likes the excessive drainage of Alderwood soils.

Other suggestions for you: Juniperus chinensis 'Spartan' or Juniperus scopulorum 'Wichita Blue'. These would handle the dry rocky soil well, as well as being unpalatable to deer. They are also dense, tall and narrow. My only concern with the scopulorum would be the silvery blue color would not serve as well as a visual backdrop.
Note- my established Italian Cypress were burned to the point of needing removal last winter. I am in Lake Forest Park on the Kenmore side. I'm guessing Woodinville gets just as cold.

There are wax myrtles in this area more than twice 12' tall. 12' is no problem for this rather rapid and vertically growing shrub, a sort of evergreen willow.

While the 'Compacta' strawberry tree of reference manual(s) is supposed to be a shy-flowering dwarf what passes for it in the Pacific Coastal nursery trade is clearly an aggregate of seedlings of varying characteristics. 12' should be no problem for these. What is a problem for this tree is cold, damp or inadequately exposed situations, same as most other species in the genus.

A damp frost pocket out Woodinville way might be problematic for the wax myrtle also. What particular exposure and air and soil drainage your lot offers is fundamentally important to what you will be able to produce attractive plantings with.