Some really good archers get string slap; that's why they make arm guards, I guess. However, there are a couple of things you might check. How tight are you gripping the bow? If you grip the bow loosely (but not so loose that you have to grab it to keep it from falling out of your hands when you shoot it) you are less likely to have string slap. If you are pushing correctly with your bow arm, you are less likely to have string slap. If you shoot from a slightly open stance, you are less likely to have string slap. But if your stance is too open, it can lead to poor form, so search on this forum for Terry's clock to check that your body is in good allignment. If your bow wrist is turned inward too much, it can lead to string slap. Try to shoot with a straight wrist rather than cocking your wrist into the bow. If you are shooting a recurve that is braced a little higher, it is easier to avoid string slap than with a lower braced longbow. If your bow arm is not locked, it is less likely to have string slap. But some good archers shoot with their bow arm locked. Apparently, some medieval archers thought it was a badge of honor to have a calouse on the inside of their bow forearm, but I don't think we're into that these days.