I reckon it's a dog stinkhorn. Mutinus caninus (what a great name).
Look! Half a potato! Apparently these are called the "eggs":
I haven't yet seen these things (I suspect the dog obliterated them), but aren't they utterly, magnificantly phallic?
"It has some disgusting mushroom fruit that looks like a dog d*ck with the tip dipped in sh*t."
Although I've never actually seen one of these dog-dick thingies. Anyway this one will be bagged and binned tomorrow. Apparently they don't normally sprout dicks until July, so it might still have been at the egg stage. Gawd knows.