female fox urine will kill plants instantly. Males less so. It because of the ammonia content. Anything organic containing blood and/or bonemeal will cause them to dig it up (They think there is a corpse underneath). There are 2 reliable ways of deterring them. One is Aluminium sulphate, but it needs re-applying after rain. The other is clear plastic 2-litre bottles, half-filled with water, placed on their sides. I don't know how it works, it just does. I suspect it's either the reflection or when they move them, it seems as if they have a life of their own. Spring is the worst time as they teach their young to dig for grubs, wire-worms etc. The trouble is, when they start to dig in one spot, they tend to return to it.