I got so sick and tired of pigeons, caterpillars and other pests destroying my vegetables that I built a cage to go over the top of the cabbage bed and covered it with horticultural fleece. Rain goes through the fleece, so you don't need to lift it to water underneath like you do with glass cloches.
Then my promising crops of peas, carrots and onions were all ruined by horrible maggoty things, so I now keep them covered with fleece too. The climate under the fleece seems to give them a boost early in the year, when the nights are still cold. It doesn't look very pretty, but neither do peas, onions and carrots that have maggots tunnelling through them.
On the subject of foul maggoty creatures, I've given up on blackberries and raspberries because the raspberry beetles are legion in this part of the country. I was told that they lay eggs on the fertilised flowers, which hatch in time for the maggots feast inside the developing fruit, and then they drop off and pupate in the soil around the base of the plants, climbing up the next year to lay their eggs in the flowers and continue their disgusting life cycle.
A bowl of raspberries with tiny transparent maggots squirming around is not going to temp anyone to eat more fresh fruit. I've heard that some people make jam with them, claiming that the maggots are made from fruit too, so don't count, but I don't fancy it. Or that you can grow each individual cane in a bucket of soil, and change the soil every year, so that any beetle chrysalises are got rid of, but then you'd have to be forever watering those buckets, it seems like a lot of hard work.
To anyone else who has a problem with raspberry beetles ruining their raspberry and blackberry crops, I heartily recommend growing Japanese wineberries instead. They are like tiny raspberries, little jewels, that taste lovely and look very pretty used as decorations. The best thing about them is that they thwart the attack of the raspberry beetles by hiding their fertilised flowers inside a closed calyx, so the beetles can't get at them to lay their eggs. I started out with one vine, and discovered that tips of the vine put out roots when they were allowed to touch the earth. So I now have 10 meters of vines trained on wires against the north east facing garden fence. The calyxes don't open until the berries are ready to ripen, and the vines fruit for at least 6-8 weeks every summer, producing more fruit than I have space for in the freezer. I bought a dehydrator last year, thinking I'd turn them into little dried snacks, but they took much longer than any other fruit (including big juicy things like pineapple and mango slices), I think they have some kind of sticky, waxy coating that isn't obvious until you try to dry them. So next year I'm going to moosh them in the liquidiser and try to make fruit leather instead.