Trav,
You said you were going to use dirtholes, so this is what I do in that situation.
The urine/lure goes behind the trap on the backing. The fox has to cross your trap in order to get a good smell. Urine can be applied to an older dry fox turd at the set. In this situation, the turd is used a guide to direct the fox to step on the pan.
Your backing can be many things. A clump of grass, a bone, a chunk of wood, a raised bank, or a small animal skull. And these are just a few suggestions. Each trap location can mean a different type of backing.
The bait goes down in the hole and I usually plug the hole with a wad of grass. Lure and urine are the smells which get a fox to the trap location. Bait is what holds him there long enough to get caught.
Randy