How about a low wall with hedge shrubs planted in the top?

A few years ago I did some outdoor courses at a horse stud and didn't even know there was a busy by-pass only about 50 yards away thanks to some retaining banks and thick hedges - but was told it's sometimes loud in winter after leaf fall. Bearing that in mind, evergreens seem sensible, at least in part.

We built our own stable yard from scratch, so I've learned that brickwork is a doddle. There's only three main rules. First is footings must be right for the soil type, wall height and any surrounding planting. A local builder will offer advice on those fronts. The second is that piers must be built in at distances capable of strengthening the wall depending on it's height. Putting piers at both sides is a good idea. The third is really important, but often forgotten - mortar strength is vital. It must be weaker than the bricks, partly so that if frost damages the wall the mortar will give before the bricks (it's easier to fix, after all!) and partly so that when the bricks come to be re-used they are almost self cleaning.

We had a builder come and give us quotes for our yard and while he was there picked his brains about pier distance and so on, then cheekily built it all ourselves! A gardening book gave mortar mixes and I think we've pretty much cracked the whole thing now just by practice and a bit more practice. To make the stables cheap we used concrete blocks, seconds from the housing trade, and rendered it all. Looks great painted, but will need repainting in places within 5 years. Coloured render would have been more sensible, but you live and learn! Most of the walls are rendered block for the first course, then old bricks from anything knocked down locally. The old bricks are weak but utterly gorgous! They look fantastic once up and really set the place off within the countryside. Being odd sizes and shapes means they are easy to use because any bits I've built off level are soon hidden anyway!

Having said all that, if I were you I would be tempted to plant a nice hedge with maybe some wall to grow things against. The wind filtering of a hedge is better and you won't get the nasty eddies that walls make on their leeward side, nor frost pockets.

Hope it all works out well.