Help identifying night visitor in garden.

Hi everyone,

I think we have a new visitor in our garden which left us 'a present' in my vegetable box last night.
I can't figure out what it is. We have never had cats around as we have two small dogs, so I don't think it is a cat. I also don't think it is any of the dogs, as,  it does not look like it and they would not dig/use a small 'latrine'. They go on the lawn...

We have noticed digging in this place before but never any 'left overs'. We thought it might be the birds digging. When I 'patted' the area down, the first time I noticed the digging, it was a very foul smell, not like earth or compost would be.

I have also noticed some digging around other areas, especially where it has been new planting.

Any idea?