The world trail builders told me that cornhill at buller was a mess after one of the races run in wet conditions . They had to do a lot of work to fix it up. One benefit though is that they made the descent a lot better, similar to stonefly, while fixing up the trail. I'm not sure you can make a completely sustainable trail. Maintenance is always going to be needed.well if trails are built sustainably, i'm not saying Buxton trails are unsustainable, then they should be able to withstand races and use. Look at Mt Buller for example, Glen Jacobs trail, sustainable trail, cops a battering and holds up fine...