Avoiding Carrot Root Fly

Growing your own carrots is easy and rewarding - nothing beats the sweet taste of freshly lifted young carrots. There are many varieties of all shapes and sizes and all are easy to grow. I grow the 'Early Nantes' variety which is a slender finger length carrot.
The only problem you are likely to encounter is the carrot root fly. The adult flies first lay their eggs in May/June and then lay a second batch in July/August. The eggs hatch to produce small maggots which tunnel into the roots. The adult fly is attracted to the carrots by the smell released from fresh leaves so it is best if you handle the leaves as little as possible. It helps if you don't sow the carrots too thickly so there are fewer seedlings to thin out. 
One way of deterring the adult fly without using chemicals is by interspersing rows of carrots with rows of onions. The smell of the onions allegedly disguises the smell of the carrot leaves. I haven't tried this method as I have limited space to grow root crops in my vegetable patch. So I decided to try a different method. I saw a television programme which featured someone who had previously suffered a lot of problems with carrot root fly and who found a simple chemical free solution. Evidently the flies will fly at a certain height and this person solved the problem by growing their carrots in a barrel about 3 feet tall, above the height at which the adult carrot fly travels.
I have managed to get hold of an old 45 gallon plastic drum which I have filled with soil and planted with carrots. I tried this for the first time last year and had a reasonable crop so I hope to repeat that success this year.