Smart As A Front Porch Dog

Harold told me today that someone we were talking about was "as smart as a front porch dog."

I have no idea what the difference between a 'front porch dog' and a 'back porch dog' is.  Under the porch dogs I understand.  You drive up to a house in the country and here they come barking at you from under the porch.

'As smart as a front porch dog' calls to be in a story.

I love Haroldisms and Suzisms.