1. To peel prickly pears, cut off a thin slice from either end, then cut a slit into the skin of each prickly pear from top to bottom. Peel off the skin and roughly chop the fruit.
2. In a blender puree prickly pear fruit until smooth. Strain through a fine mesh sieve to remove seeds.
3. In a large measuring cup combine prickly pear puree, tequila, lime juice, triple sec, and agave and stir well.
4. For each margarita, run lime wedge around the rim of a glass, then rim the glass with salt. Fill glass with ice cubes.
5. To a cocktail shaker ⅔ full of ice add 4oz of prickly pear margarita mixture. Shake vigorously until well chilled, about 12 seconds. Strain into rimmed glass and garnish with a lime wheel. Repeat to make more cocktails.