I just woke up, so I'm not to creative right now...but my husband has one for Roxy. It may sound mean, but Roxy is Mike's favorite. He just likes making fun of her because she isn't very bright.

Rox, Rox, dumb as rocks...
She falls down when she walks...
runs to the backdoor
when the frontdoor knocks...

I don't remember his one for Dusty, but it's starts off
as

Dust, Dust, Dusty Dirt...