Copyright 2007 Houston Chronicle On any Sunday morning, sanctuary doors of churches that line Main Street and nearby thoroughfares swing open to welcome thousands of faithful who come to worship in some of the city's oldest, most prominent religious institutions. But at other times in the week, doors may be locked tight, windows latched and grounds and hallways patrolled by burly uniformed guards. -snip- And though the security problems may be most pronounced at the city's downtown-area churches, their suburban counterparts often implement equally stringent safety measures to protect their property and congregants. -snip-