CAMP FALLUJAH, Iraq-American commanders are fully aware that Iraq's insurgents exploit their policy of employing locals on the U.S. military bases, but insist the practice will not stop, though some security measures may be tightened.The vulnerability of the American stance was exposed on Dec. 21, when an Iraqi suicide bomber dresed in a military uniform, detonated his explosives at a mess hall at Forward Operating Base Marez in Mosul, killing 22 people, including 14 U.S. servicmembers.