Last year our carrots were ruined by carrot root fly.

It was probably my fault - because I had been adding discarded
root-fly-infested bits of carrot to the compost heap - so that probably
went back into the earth.

Anyway - I want to do better this year.
Someone on Gardeners Question Time recommended growing carrots under
fleece for the whole of their lives.

But if you do that, what about harvesting the carrots?
Won't the flies get in then?
We harvest only half-a-dozen carrots at a time - just enough for a meal
- and so we can't dig up a whole fleece worth of carrots at one go.

Any suggestions?
--
Chris