I recently visited a country estate in the UK. The gardens had a number of large beds and the paths through these beds where all lined with low (2 foot or so) fences to create the barrier. The really clever thing was that these "fences" where made up of apple and pear trees, trained to grow along a series of supporting posts. The trees where covered in large, juicy fruit and from what I could tell each tree was trained for 10's of feet in each direction to form the fence.
I have never seen this done before and wondered if anyone here had any ideas for varieties of apple and pear trees that would be suitable to grow in this way to eventually form the main paths of my allotment patch. I am also looking for any suggestion on the best techniques for getting this kind of long low horizontal training?