The fact that you have had both urinating posts and dirt holes dug up does point to something being contaminated. if you are sure your intial dying and waxing process is not suspect, I would backtrack in your mind the process you followed in storing your equiptment and using it. Your sifter, trowel, wax paper, traps,trap stakes where you got your dirt etc.
Another posibility which I ran into when I was younger was the fox and coyote in my area had been trapped by someone who used a certain brand of lure and had learned to associate it with a trap so they would immediately become suspicious and dig or nose the trap out. If you can't find a problem with your hardware keep this in mind if it makes sense in your particular situation