I have been told of a a deterrent for cabbage white butterflies: To place a large white butterfly hanging in her garden and the real ones wouldn't go near her cabbages (etc).
This woman got told it by a friend, who swore it works. She tried it and she says it works. (She said she couldn't find a large white butterfly so hung two supermarket shopping bags in a sort of butterfly shape instead.)
It sounds a bit like that theory that if you left 1.5 litre pop bottles lying around your front lawn, then dogs wouldn't come into your property. We all know THAT didn't work, and there's no reason why this idea should but it wouldn't hurt to give this one a try and could even be attractive!
It would be possible to staple two 2 litre ice cream container lids together in a butterfly shape and suspend that in your garden.
What do you think? Anyone going to give it a go?