Sounds like you need to rearrange the fender so it sits further forward (easy on SKS fenders until you've clamped down the mounts, then next to impossible). Then, as others have said, mudflaps. Mine's made of an old shampoo bottle that's about 10-11 years old. I'm so embarassed by it, I'm going to replace it as soon as it falls off. But it hasn't yet.