Miscantheus x giganteus is a variety of miscanthus grass that grows 12-15 ft tall by its 2nd year and is not invasive. It will not spread beyond where you’ve planted it. This is not true of every miscanthus variety, most of the ornamental varieties of miscanthus that you see in landscaping centers can spread by seed. The specific variety I’m recommending is a sterile hybrid and it will not spread. I’ve planted 3500 acres of it, I know this to be true.
It’s quite attractive, too. In the winter it will go dormant and be yellow & dry, but stays upright so you still have that privacy screen. In the late winter / early spring, you can just bushhog it and the next season’s growth will jump right up. You don’t have to bushhog–new growth will just grow up/around the dry stuff–but I think it looks nicer.
Hardy up to Zone 5b, though in that zone it’s a bit vulnerable to a winter kill its first season if you have a very cold winter. Mulching would help that, but of course that adds cost. I wouldn’t rule out Zone 5a or even 4, if you’re willing to take the risk and if you get through its first winter you’re probably ok. Tolerates most soil conditions as long as it’s not too sandy/dry or constantly boggy.
ETA: not toxic and even though it’s a grass, grazing animals and deer don’t bother with it. The leaves are quite sturdy and a bit sharp edged, so they quickly decide it’s just not good grazing.
here’s what it looks like in winter and summer
It’s planted as a rhyzome so you have to dig a hole and cover. More time consuming to plant than just scattering seed, but way easier than trees/shrubs. If I were doing a 2.5ac perimeter, I’d rent a trencher and do it that way.
Here’s a possible supplier. Hope this helps!!