there lies the big question
we have all suffered under the slug or snail or Caterpillar and on and on
there is no real defence against this other than either copper rings around the bottom of the root slug pellets
caterpillars are the big bug bearer hear on my plot keeping the white moth off everything if your not netting its difficult rhubarb leaf tea tends to help over them as they dont like the smell or the taste
its a up hill struggle though if you find the perfect answer id love to know i try different things all the time and still haven't got to the bottom of it
sorry cant be of some definitive help