Landlords in and around San Diego do not seem too worried about the parlous state of technology firms in the apparently waning US economy. Even though Silicon Valley companies like Sun Microsystems are looking for office space and many communications companies have followed Qualcomm, Nokia, Ericsson and Motorola on the trail to San Diego, the dot.com meltdown will not concern the city's cautious landlords. They have reportedly taken to asking dot.com companies to provide substantial letters of credit to make sure the rent is paid.