The next phase, cross-country, requires both horse and rider to be in excellent physical shape and to be brave and trusting of each other. This phase consists of approximately 12–20 fences (lower levels), or 30–40 at the higher levels, placed on a long outdoor circuit. These fences consist of very solidly built natural objects (logs, stone walls, etc.) as well as various obstacles such as ponds and streams, ditches, drops and banks, and combinations including several jumping efforts based on objects that would commonly occur in the countryside. Sometimes, particularly at higher levels, fences are designed that would not normally occur in nature. However, these are still designed to be as solid as more natural obstacles. Safety regulations mean that some obstacles are now being built with a "frangible pin system", allowing part or all of the jump to collapse if hit with enough impact. Speed is also a factor, with the rider required to cross the finish line within a certain time frame (optimum time). Crossing the finish line after the optimum time results in penalties for each second over. At lower levels, there is also a speed fault time, where penalties are incurred for horse and rider pairs completing the course too quickly. For every "disobedience" (refusal or run-out of a jump) a horse and rider incur on course, penalties will be added to their dressage score. After four disobediences altogether or three disobediences at one fence the pair is eliminated, meaning they can no longer participate in the competition. A horse and rider pair can also be eliminated for going off course, for example missing a fence. If the horses shoulder and hind-quarter touch the ground, mandatory retirement is taken and they are not allowed to participate further in the competition. If the rider falls off the horse they are eliminated. However, in the US this rule is currently being revised for the Novice level and below. The penalties for disobediences on cross-country are weighted severely relative to the other phases of competition to emphasize the importance of courage, endurance, and athleticism. Fitness is required as the time allowed will require a strong canter at the lower levels, all the way to a strong gallop at the higher events.