How dense do you want it. For fast dense privacy, you can't beat plain boring Ligustrum japonicum. It's common because it's reliable. It makes a nice dark background for more interesting plants. Prunus caroliniana is pretty dense but you need to tip-prune it to get it really dense. It's pretty fast. They get really tall after a couple of decades. Most of the Pitts tenuifoliums are not super dense. Monrovia has a new introduction called 'Tasman Ruffles' I think that is supposed to be much more dense. Pitts are pretty fast, but not as fast as Ligustrum if watered. They can be a little fussy, and aphids, scale can be a problem. Beautiful, though.

I thought Viburnum Odoratissimum would be a good idea as a fence line hedge. Planted a line of them to cover 120' front property line. They have been awful. Disease prone, all sorts of insect pest, and likely a lot of the problems has been caused by the long term drought. These things are not as drought tolerant as reported, not here. Not on this sand soil I have in southern Pinellas. In fact after looking around at where these things are used, due to how common they are and price they are a favorite at shopping centers and gov. buildings I an not unique with these pitiful things. All over they are sparse in growth with a ton of dead branches. Again I suspect this is because they are not getting enough water. I will never use this junk again. They have struggled for 8 yrs and only one of the 12 has done goodd. Aphids, thrips, scale, you name it they get it when they do grow like now. What I have found working very well though it must be trimmed is the small tree/shrub, the native wax myrtle. Incredible how it thrives wet or dry and when trimmed produces a thick bush shrub privacy effect. However left on its own without trimming it will get a bit more tree like and that is fine too. It will sucker some but comparing these two plants for my purpose hands down winner is the wax myrtle.

Seconding Arborvitae for your area (I'm in northern Illinois, about an hour from you). Proper name: northern white-cedar --- Cupressaceae Thuja occidentalis L Cultivars: 'Aurea' - A golden globe that needs little shearing. 'Boisbraind' - A plant 10 feet tall with dark green, burn resistant foliage. 'Brabant' - This cultivar tends to form one central leader thus minimizing stem damage from winter snows. 'Brandon' - A fast-growing, cone-shaped plant about 15 feet tall and 4 feet wide. Reported as suitable for use on harsh sites. 'Chalet' - A narrow plant with a rounded top and lime- green foliage. It will be 10 to 15 feet tall. 'Compact American' - A compact, pyramidal form reaching a height of 25 feet and a spread of 8 feet. 'Danica' - A slow-growing, compact globe with dark green foliage. 'Degroot's Spire' - A narrow, columnar form. 'Douglasii Pyramidalis' - A dense, columnar form with twisted dark green foliage. 'Elegantissima' - A slow-growing, dense plant with yellow branch tips. 'Filiformis' - A pendulous plant with long, thread-like branchlets and bright green new growth. 'George Peabody' - A broad, upright plant with yellow foliage. The foliage becomes more orange in winter. 'Gold Cargo' - A cultivar with gold foliage that is reported to resist winterburn. The plant can be 25 feet tall and 6 feet wide. 'Golden' - A broad, upright form with bright yellow new growth. 'Golden Globe' - A uniform oval with foliage a soft yellow. 'Hetz Midget' - A slow-growing, compact plant. 'Hetz Wintergreen' - A narrow, upright form reaching a height of 60 feet. 'Holmstrup' - Dark green foliage that holds its color in winter. Broadly pyramidal. 'Little Gem' - A globe-shaped plant reaching a height of about 3 feet. 'Little Giant' - A slow-growing, globe-shaped plant with bright green foliage all year. 'Masonic' - Pyramidal form about 25 feet tall and 5 feet wide. 'Niagara Compact' - A globe-shaped plant more compact than 'Woodwardii'. 'Nigra' - A symmetrical form with good dark green foliage color. 'Pendula' - An open, weeping form with dark green foliage. 'Pygmy Globe' - A dwarf, globe-shaped plant with bright green foliage. Needs little shearing. 'Pyramidalis' - A narrow, columnar plant often used for screens. 'Rheingold' - Yellow foliage that becomes orange yellow in winter. 'Sherman' - A pyramidal form reaching a height of 30 feet and a spread of 12 feet. 'Sherwood Moss' - A dwarf plant 4 to 6 feet tall. 'Smaragd' ('Emerald') - Narrow habit with glossy green summer color. Reported as resistant to spider mites. Plants will be about 15 feet tall and 4 feet wide. 'Sudworthii' - Upright, broad plant with yellow foliage. 'Sunkist' - A compact, broad plant with orange-yellow foliage. 'Techny' ('Mission') - A fast-growing plant with dark green foliage. Usually about 15 feet tall. 'Tiny Tim' - A compact, upright mounding plant. 'Umbraculifera' - A rounded, irregular plant, nearly 3 feet tall and 5 feet wide. 'Unicorn' - A narrowly compact plant with dark green foliage. 'Wareana' - A slow-growing, broadly upright plant. 'Wintergreen' - A pyramidal form reaching a height of 30 feet that retains good green color in winter. 'Woodwardii' - A rounded form that retains its shape without shearing. 'Yellow Ribbon' - A narrow, upright habit is combined with yellow foliage all year.

It depends some on your dog, but I wouldn't count on a hedge to keep a dog in. At the least it will need a wire mesh fence in the inside of the hedge to keep the dog contained until the plants grow together. Even a well grown, mature hedge may have some gaps near the base which a dog could slide through, so it may continue to need a wire fence for the first two or three feet. This request may be a bit of a problem: "shaped like a box (not spherical and not pyramidal)" since in order to maintain dense foliage near the bottom of a hedge, you will need to taper it some so that the upper parts of the hedge don't shade out the lower parts of the hedge. To maintain a boxy tapered shape rather than a more rounded shape will require pruning to give you flat sides. Do you have deer? If not, there are forms of Thuja occidentalis that will stay shorter and will grow together to make a good hedge. I don't personally have experience with how they take to pruning since I like my plants unpruned for the most part. I have 'Sunkist' (green-gold) which will be easy to maintain in the 6'-10' range for quite some time based on mine as they seem to have slowed considerably at about 5'. I bought plants in the fall of 2007 at about 3'. As individual plants they are a bit floppy in heavy snow/ice situations, but that may be less of an issue with a hedge. 'Techny' is dark green and grows to 10'-15', and I have seen photos of it pruned into a hedge. I planted mine at about 4' in the fall of 2007 and they are about 6' now. I imagine that you can find other selections of this native evergreen that are dwarf in size compared to the regular species (which grows to around 40'.) If you have deer issues they aren't a good choice, but in my heavily wooded rural area, they haven't been bothered. spring 2010 From evergreen shrubs spring 2014 From evergreen shrubs Another possible choice to look into is a really hardy Rhododendron, though they will have a more rounded form and IMO don't look great pruned into boxy shapes and will make a more gently flowing shaped hedge. They will have the added benefit of spring flowers if you don't prune them. In really cold weather they don't provide a lot of sight privacy since the leaves tend to curl up, but most folks don't require a lot of privacy when the temperatures are below 15 degrees. The link below will take you to a search page from the American Rhododendron Society which allows you to put in height preferences. On left side of photoPJM rhododendrons in 3/4 shade (so not as dense as full sun,) about 5' at 6 or 7 years in the ground from >1' when planted. From evergreen shrubs You could ask this question on the shrub forum or the conifer forum for other suggestions beyond what you get here. It also might be worth visiting local nurseries (not big box stores which often have poor or inaccurate info and plants that may not be hardy here) to see what they have in stock that would fit your requirements. They could most probably order more to complete your hedge as it will take a rather large number of plants. Here is a link that might be useful: Rhododendron Plant Search