I made this Thick Clefthoof Leather farming guide to help out players who want to farm the leathers instead of buying them from the Auction House.
There were no major changes to Thick Clefthoof Leather drop rates, so this guide can be used for Burning Crusade Classic (TBC) and Retail WoW. But, if you play Retail WoW, you should learn Outland Skinning from Seymour in Shattrath City before they start farming, or you will get fewer leathers.
Thick Clefthoof Leather
The best place to farm Thick Clefthoof Leather is around Garadar in Nagrand. There are plenty of Clefthoof Bulls roaming around the area, and they have the highest chance to drop Thick Clefthoof Leather.
If you can't farm around Garadar because too many people are farming there, you can try the Clefthoof Bulls to the east of Oshu'Gun. There aren't that many there, so you will have to wait for respawns if you kill them too fast. Make sure to kill every Clefthoofs and Clefthoof Calfs there too. They have a much lower drop rate but often roam in packs, so it's easy to kill them if you have good AoE damage.
You can also farm the Clefthoofs around the marked area. These have a much lower drop rate, so you should only farm these if the other farming places are taken.