Quarter the ducks and remove the backbones. Cut and trim off as much fat as possible. Grind any excess skin and all the fat in a food processor, place in a deep saucepan with 1 cup water and render the fat (simmer it over low heat for about 45 minutes, uncovered), strain, and reserve.
Cut each breast into halves with the wings attached. Roll each piece of duck in the salt and place it in a large stainless glass or earthen bowl. Sprinkle each piece of duck with a mixture of the shallots, herbs, and spices and scatter any remaining salt over the top. Cover loosely and refrigerate 24 hours. NOTE: This may be cut down to a few hours if it is to be eaten within a week or two.
Rinse quickly, then wipe the pieces of duck to remove all the salt, herbs, spices, and liquid.
Heat the strained fat in a deep, wide kettle. Add the duck, 1/2 cup of water, the halved garlic head, and enough rendered poultry or pork fat to cover. Bring the mixture to a boil. Lower heat and cook at a simmer for 1 1/2 hours, or until the duck flesh can be easily pierced with a straw. Do not let the mixture boil.
Remove the duck, drain and discard any loose bones. Strain the warmed fat. Put about 1 cup of warmed fat into each of the bowls or mason jars intended for storage of the confit and cool in order to congeal the fat.
Arrange the duck pieces in the containers without compacting them. Strain the remaining fat, tepid but not hot, over the duck to cover. The pieces of duck must be completely submerged in the fat. Cover and chill until solid. Cover with a layer of melted lard. Cover tightly with a glass top or with plastic wrap and store in a cool place such as a cold cellar or the refrigerator. Leave to ripen at least 1 month. It keeps well for 6 months.
To use the confit, set the jars or bowl in a warm oven. When the fat softens, remove pieces desired. Return jar or bowl to the refrigerator. Be sure all of the remaining pieces are covered with fat. The duck can be served at room temperature or warmed in an oven, then Sauteed to crisp the skin.