oooch wot you mean by 'wrecks'? rubs raw? r u wearing shorts?
Shin guards 'would' b a good investment.
But for simple rubbing, try getting some athletic knee supports ...chemists, boots prob even a big supermarket
If you look closely at some of the Walk for life pix you will see such items as sox, elbow pads, bandanas and even pillow cases to reduce rubbing!! Ive even used tea towels