Easiest way I've found, drag something out side the kennel, out of sight, and see which one picks it up. For dogs u want catchy, power tools, and lawn mowers show wonders. Do some work around them. Of they won't back up from or bark at a chainsaw or law mower, they normally won't back up from a pig lol.
Not full proof but have shown true a lot.
Makes sense! Might have to try the dragging technique one time