That isn't the deadly poisonous herb but a shrub of the species Tsuga. As a slow-growing tree, hemlock can grow to over 100 feet tall, but it's usually allowed to grow to about eight feet tall as a hedge. It's excellent to place around patios or pools because it tolerates shade a bit better than over evergreens.
This familiar hedge plant is deciduous or semi-evergreen. The oval leaf privet is the variety most commonly used for privacy hedges. It produces panicles of pretty white flowers, but some people find the smell of the flowers unpleasant. Also, the fruit is toxic to humans but suitable for birds. That makes it an excellent hedge to attract birds. It's also a food plant for many species of butterflies and moths.
Boxwood not only provides privacy, but its dense, small leaves make great noise reducers. The leaves are also aromatic. Usually, boxwoods grow to between three and six feet, but some can grow to 10 feet tall.
Other shrubs that provide good hedges are arborvitae, yew, holly, viburnum, and euonymus. One thing about fences is that it takes a while before they grow tall enough to provide privacy. That is true unless the homeowner buys all the plants entirely built, but the cost of that is prohibitive for most people. The hedge can be staggered or straight. Before the seedlings are planted, the gardener should mark the spaces with stakes. With a staggered fence, you should make a straight line with a string line, and you should place the stakes on either side of the plant. It would help if you planted the holes for the seedlings as thick and twice as wide as their containers and their root balls. You should then ease the container away from the plant, and you should loosen the roots. If they've formed a tight ball, you can trim them. It would help if you placed the rootball into the hole, and you should tamp the so around it. Then, you should water the plant thoroughly. Depending on how quickly the plants grow and how well they're cared for, a thick, tall hedge should emerge over a few years.