<Li> Liverpool: a ditch or large tray of water under a vertical or oxer </Li> <Li> Joker--a tricky fence comprising only a rustic (or unpainted) rail and two wings wherein the lack of filler makes it difficult for a horse to judge their proximity to the fence as well as the fence's height, making it a tricky obstacle usually found only in the upper divisions, and illegal in some competitions </Li> <P> At international level competitions that are governed by FEI rules, fence heights begin at 1.50 metres (4 ft 11 in). Other competition levels are given different names in different nations, but are based primarily on the height and spread of fences </P> <P> In the United States, jumping levels range from 0--9 as follows: USEF Jumper Levels </P>

Which is not one of the four basic rules for riding