You chaps seem to know about these things...

This morning I found four dead frogs in the garden, heads chewed by either
fox or cat, I presume. I also found four corresponding holes - three in
the border, and one in the loose compost in a large pot - muddy frog body to
the side.

This happened last year as well, and I'm guessing that the frogs had been
hibernating in the top few inches and were dug out by the cat/fox, does
anyone have a better explanation?

Anne.

were dug out by the cat/fox

Digging prey out really doesn't sound like cat-type behaviour ... more like
dog-type, therefore I would suggest fox.

Best,

- h