I got pretty dejected last year after numerous attacks carried out by what I assume were fox cubs (they had yet to learn the difference between chicken poo fertiliser and a good meal, and also like to play - they flattened and ripped holes in the enviromesh covering the leeks and carrots, dug up and killed my outdoor cucumbers which were in a planter, and almost uprooted one of my 15 year-old blueberry bushes.)
This year (and I'm typing one-handed so I can keep the other one on my wooden desk!) although I've seen an adult fox in my garden, there has been no damage so far...
They are such agile and sometimes determined animals it's hard to keep crops safe using normal gardening methods.
Fertilisers like blood, fish and bone are a definite no-no, and you might consider using growmore rather than chicken poo as a general fertiliser if you don't already.
If I'd had a repeat performance this year, I would have invested in an PIR activated water sprayer in an attempt to deter them, although that does require a mains hose connection of course.
Good luck, hope they get bored with sweetcorn PDQ!