excrement of any animal (cats work best, simply find a litter box and scoop a little)
Place the energy signature (or photo, or sigil) in between two pieces of the moldy bread. Mash it together and round it so the energy signature is enveloped completely in the powers of decay. Place at the bottom of the cauldron. Then add the animal excrement and, if discovered, any items to which the enemy has an allergic reaction.
Stir the noxious ingredients in a widdershins motion. Vocalize your contempt for the enemy without being self-conscious. Shout, scream, stir up as much hate as you possibly can and direct it to the fetish for as long as can be sustained. If you wish, visualize the fetish as the enemy's head and mock striking it or make flailing gestures at it and strain the muscles in your hands and fingers as you do so.
The best time for this, of course, is the later phases of the waning moon. If you wish to add archetypal energy to this, out under the waning moon, invoke or assume the god-form of Saturn or any other deity of death you'd like and ask Hir to bless your intentions. If you assume the god-form of the deity in question, become a suitable conduit of that energy and direct it toward the fetish and visualize it mingling with the energy of your own hatred already there. This is very potent as you are including macrocosmic energy with microcosmic energy.
Then leave the fetish on the property or doorstep of the adversary. If this is not reasonably practical (if they live far away, for example) you can just leave the fetish out under the waning moon and astrally bring the etheric substance of the fetish to their home. Banish with laughter or ground with a good meal and forget it.