Ted,

You want to show the client how bad things are with the rodent problem do this.

Turn out all the lights as much as possible or close off a few doors to a room to darken it as much as possible.

Pull out one of those black light fixtures and plug it in.

You'll see what appears to be yellow-greenish streaks all across the floors and surfaces.

This is where the little varmit is urinating as he is running through the home.

They do make some flashlights that are used by PCO's for this purpose.

rick