Covering them is by far the easiest way:
I have to raise the 2nd bed netting support because thisis an older photo and now they are pushing against the top. If the leaves are pressed up against the netting, the butterflies and moths can get lucky and lay their eggs through the netting.
On the other hand, the netting also keeps out the beneficial wasps and flies that would plasticize the caterpillars or wasps and birds that would pluck them off to feed them to their young.
Best companions are planted earlier -- the blooms of radish, arugula, mustard, cilantro, chervil, etc. that bolt when it's gets hot attract the predatory beneficial insects. Onions and garlic are said to help. Some people make garlic and hot pepper spray, though I haven't tried that. (I tend to dislike any spray because they can affect the flavor and I get frustrated trying to wash them off.)
But once the infestation is beyond reasonable control by hand picking, I agree Bt for caterpillars is the best as long as it is used carefully so as not to poison the butterflies and moth caterpillars that you WANT to have living in and around your garden.