Hands up. Who ate my cabbages?

Something crawled under the cloches, crawled under the plastic covering and ate my cabbages. Voles or shrews I expect

My plot is in a field, unfenced, open countryside and how can I prevent voles or shrews or mice, it wasn't pigeons, from chewing the cabbages.?

If anyone has any tips please pass them on.

First person who says get a cat wins the 'I'm not taking this seriously' badge.

Earth up the sides of your cloches or put lengths of something heavy so the critturs can't get underneath.