I'm making the assumption that the physical barrier and time is more important to you than a stylish, trendy choice. I'm also assuming you want super-dense growth, not airy, see-through growth. If it was me in that not very appealing situation of homeless people pooping on the lawn, I would go with boring, plain, common, utterly reliable old Privet, Ligustrum Japonicum, available in 1 gallons at any Home Depot for about $5 each. Yes they are boring, and horribly common, but they are common for a very good reason: they make a dense, tough hedge FAST. Plant them at 3' centers and you'll have a substantial physical barrier in a year. Water them generously and feed them a couple of times and tip the stems growing outwards back as they grow. Ligustrum well watered and fed will quickly grow 6'-8' stems that arch outwards and wave above the rest of the original juvenile (baby plant) growth. Temporarily stake these stems straight UP or almost straight up with bamboo stakes, creating a strong basis for vertical growth. Cut them at the height you want. They will stiffen up and branch outwards. Then cut those outward growing side branches at the width you want, but reasonably you need to give them at least 30", a little more would be better. My experience is that the one gallons grow faster and stronger than the fives (at one third the price). Make totally sure you get FRESH plants that have just come in from the suppliers, not old stock that has been sitting around. If I had kids though I would also put a chain link fence of legal height (3'? 4'?) right next to the sidewalk, and grow the Privet inside that. Extra security when toys go rolling out into the street. Chain link lasts for decades. Better choice than wood and much cheaper than wrought iron or vinyl and guys who know what they are doing can install it in one day. Again I am assuming you are concerned with security first and style not so urgently and that you do not have unlimited money to spend. Almost any plant, if it gets a reasonable amount of sun during the growing season, can take winter shade. You will get better foliage density with more sun. I'm growing the Green Tower Boxwood also. I think it's a great, great plant for a screen, but it's going to be a lot slower (add 3-4 years) than Ligustrum to get really dense, and the initial cost of the plants is going to be a lot higher. They get tall fast, but they don't get dense fast. Something like that would certainly work but you have to balance out the cost & time involved as to what you want. Ligustrum planted from 1 gallons: 11 months later, nearly 6'. At about the middle of the second photo on the right, with the fence as the background, you can see the long arching stems they throw out when young. If you train those mostly upwards it will give you a narrower plant and more height faster than letting them just arch horizontally. Best of luck with your project!

Thanks, Dave. That's good to hear about the cherry laurels. It may be that seeding is a more serious problem in warmer climes, but I have a lot of ground to cover and like topsiebeezelbub can use the free plants. I'm also glad to get Pterostyrax's and your warning about ice damage problems with wax myrtle, which I hadn't heard about. I'm concerned about possible winter leaf burn making them unattractive in winter here in 7A/B, but given their extremely fast growth rate and positioning within a shrub border (once one grows up), I don't think occasional breakage will turn out to be an unacceptable problem. I do like their soft look, which you don't tend to find among the evergreens from colder areas. Suckering will work too, especially if it helps keep roaming deer and dogs out of my garden, though I'm not pinning any big hopes on that one. Dave, I've also been meaning to go take a few snips of a particularly nice mature shrub down at the post office. I haven't identified it, but I figure that doesn't matter when I can see what it's grown into surrounded with concrete. Lisa, pineapple guava and pittosporum are a couple of the more tender ones alluded to--both need special protection here and can still be lost in bad winters. Once my house is built, tho, I'm going to try to find a protected corner for the guava as it is lovely. It's doing well on a masonry wall at Vines Botanic Garden in South Gwinnett. Pittosporum is planted at every gas station and McDonald's in California, so I'm not so in love with it, handsome and serviceable though it is.

Larry - BLE is Broad Leaved Evergreen. In the States the word 'evergreen' appears to be generally used for conifers so they distinguish between them and other evergreens. This is partly, I imagine, because in many areas BLEs are not very common being generally less hardy than conifers. I had to learn this term on these forums since it isn't really used much over here. There are so many BLEs here and they are so much more popular in gardens than conifers, that 'evergreen' covers them.

i dont think 2 nor 3 feet is sufficient for a 12 to 15 foot tall tree ... shall we presume it would be a box with no bottom.. so they can grow into mother earth ???? and keep in mind.. no tree really stops growing at some magical height ... a pic of the spot would probably get you better suggestions ... have you discussed the encroachments with your zoning office?? ken