i once heard a veterinarian talk about this. He suggested that you play a recording of thunder at a really low volume and play with the doggy. then over time (days, weeks, months) slowly increase the volume and continue playing with the dog. Hopefully the dog begins to associate the thunder with playtime and the fear dissipates...but then when there are thunderstorms the dog may want to play....so you gotta choose the worse of two evils i suppose