Chill 2-3 glasses in your fridge or freezer 10 minutes before making the cocktail.Combine the sugar and salt and spread it on a flat bread plate. Dampen the rim of your glass with water or lime juice and dip it in the sugar/salt mixture. (Save the leftover mixture for another occasion).Combine the watermelon juice, vodka, liqueur and lime juice in a cocktail shaker. Fill the shaker with ice and shake vigorously for 6-8 times.Strain and pour the mixture into the prepared glasses and garnish with a watermelon wedge.