Hiya, I have 2 questions.... *How do I win the obstacle course at lon..

For the ranch, there are 3 heights to fences. The small ones, you don't need to accelerate. The medium ones, you might need to use a carrot. The high ones you need and carrot or two. Just practice to get the feel of the speed of Epona, so you know how fast she needs to be to jump the fences. Also, once you have one carrot left, wait until your meter replenishes to full, then accelerate up again.
Don't forget that you need to hit the fence straight on, and stay as close to the inner fence as possible.

You need the Hover Boots from the Shadow Temple to cross the sinking sand. You also need the Lens of Truth from the well dungeon in Kakariko Village (take out your Ocarina in the future in the windmill to learn the Song of Storms, then use it in the past) to see the guide to follow from flag to flag.
After you get to the Spirit Temple as an adult, use the warp song to go there as a child.
I'm not sure if you need to free all the carpenters from Gerudo Fortress first, to gain access to the desert outside.