Pak choi pests

This is my first year growing it and although it is growing to since healthy size and I have kept birds and slugs form it there is a different pest....

All the leaves look like they have been repeatedly stabbed with a very fine needle several hundred times. I forgot to take a picture or would post it.

Any ideas what it could be and what I can do about it? Is it just cosmetic and the plants edible or shall I just pull them out now?

Its the dreaded flea beetle.  Barrier mesh or insecticide.

Would it work to grow these as pick leaves and come again in trays of compost in a poly greenhouse? - that way they could escape being munched?