Was wondering how often a string needs to be replaced. I do a fair amount of shooting during the year and a lot of shooting before the season starts. My string is three years old, but doesn't show any signs of fraying, etc. I keep it waxed and have the serving replaced every year. I hate to mess with it because it shoots so well now, but I don't want to break a string either. When I replace it, what kind would be best?