Do not worry about Oleanders toxicity. my aunt has been a veterinarian in PHX for 30 years and has never seen or heard of a case of oleander poisoning. We decided against Oleanders because of the proximity to the pool, they are very messy. We instead planted a Japanese Privet hedge, total of 65 5-gal spaced 3 ft. The only main drawback is the water consumption during their first summer. Each received 5 gallons of water 5x/week. Heavy water schedule on a reliable drip is an absolute must in their first summer. Otherwise they will fry. Even with consistent deep watering, about 20% did not survive. Another tip that will greatly enhance survival and thrive is proper soil amendment. Privets do not like high PH soil (too much salt) which is very prevalent in AZ soil. Prior to planting, treat the soil w a sulfur product. this will loosen the soil and allow for maximum nutrition uptake. Ensure to continually treat the plants w products that will lower PH levels. Many synthetic fertilizers will increase PH, so look for a local organic compound meant for trees and shrubs. Our hedge has grown 4 ft in 2 years. and will grow faster now that they're established. Good luck!

I wonder if you asked the head gardener/groundsman at a botanical garden, if he/she might know of a nursery that will carry the size you are looking for? They sometimes have to fill in empty places, and also may have a 'stash' of large container plants in their back-up nursery. I wonder also, if one might plant a rapid-growing "temporary" tree to fill the light-blocking needs and act as a nursery-tree for slower growing natives? The 'temp' could be cut down after the native had reached a suitable height. Does that sound workable? Here is a link that might be useful: CA Botanical Gardens

I'd recommend summersweet clethra. It comes in white or pink, grows to about 5 or 6 feet and has fragrant flowers from about mid July to mid August. This plant has a very clean appearance even without pruning

Addison, I have no personal experience growing jack pines, because I have no areas with salt, and almost no sandy soil anywhere on my land. I live on a dirt road which never receives road salt, and the areas I'm re-foresting are a good distance from that road, behind the house. I mentioned jack pines because they seem to grow profusely in coastal areas in Maine and MA where the soil contains a good proportion of sand and salt. It does seem they grow quite large and would indeed be unsuitable for your hedge, but perhaps will grow on the ridge as you've planned. I just don't know how they do in areas with rich, un-salty soil. I like trees and shrubs to look natural as well. I never prune anything on the property, except to remove branches that are growing into our walking trails or into the path of the mower. However I don't worry much about whether a shrub or tree is native. My apples, crabapples, and lilacs (some of both are in my front yard along the road) are not native, but I doubt that the sight of these ruins whatever Vermont experience visitors might expect. Too bad for them, if so, because these trees/shrubs are ubiquitous all over the state, and impossible to avoid!