Level 2 cows in Burthorpe have 25 life points and always drop cowhide. The pen is located south of the lodestone in Burthorpe. Start killing the cows -- they respawn instantly. Since they have a fairly long death animation, kill one cow, then another, then grab the first cow's hide. This is faster than waiting for the first one to die. Once you have 28 cowhide, run slightly north to Jack Oval, who will tan them into hard leather for 3 coins each. Run further north to the Bank Gnome, bank the leather, run back to the cow pen, and repeat.