Two years ago we planted up a 10m long garden bed with 7 different citrus trained flat onto the fence. This bed faces west and is bathed in sun all day, although it is shaded from the very hot afternoon sun by a giant Chinese elm tree. They are coming along brilliantly and are in full fruit at present. It is an evergreen hedge all year round, with fragrant spring flowers and the benefit of winter fruit.. a hedge you can eat - perfect!
You can espalier any citrus that grows well in your area, this will depend on how much frost you get. We chose 'Eureka' and 'Myer' lemons, 'Tahitian' lime, 'Emperor' Mandarin and 'Arnold' Blood Orange. I'd also like to add a Ruby grapefruit and Aussie Finger Lime. 'Splitzers' where two different citrus are grafted onto the one tree are also excellent for this design, just select as many as you can fit along your fence. The citrus are planted quite close to each at 1.2 metre centres, this looks too close, but as the horizontal branches grow they will grow into each other creating a living screen in front of our ugly fence.
Train citrus flat against the wall by installing galvanized wire along the timber paling fence at 20cm heights. As each branch grows it is clipped onto the wire with green plastic 'c' shaped clips bought from the hardware store. This way you get more room in front to plant more vegetables!
Prune citrus once they've grown to the the top of the fence. Then its a matter of general citrus care: feeding them every season with citrus food, watering every month with Harvest, spraying with EcoOil to keep the pests and leaf minor at bay and trimming after fruiting.
Happy gardening :)