City officials in Fargo, keep hammering home a message of vigilance.They want residents to keep alert for any evidence of flooding, despite positive news that there's been a slight drop in water levels along the Red river.As Teri Okita reports from Fargo, they're using several lines of defense against floodwaters.It was sign to many in Fargo that you can never let your guard down ... even behind a wall of sandbags.Volunteers spotted water from the Red river pouring into a private high school ... from a leak under a floodwall. National Guard troops and city workers rushed to the scene early Sunday to help. The school president says they'll recover, but it's been a challenging week.Bruce Masselt says, "When you're fighting a flood like this, it seems like for four days in a row, you had ebbs and flows of emotions."On the opposite side of the river in Minnesota, the Coast Guard is using airboats to rescue people who did not want to evacuate. The water in some driveways of Oakport is one to two-feet deep. The National Weather Service believes the river has already crested at 41-feet, but until it drops below 38, the mayor of Fargo won't feel safe.Dennis Walacker says, "It's good news. Is it over? Not yet."Teri Okita says, "The national guard ... and even citizens ... are keeping watch over these dikes, checking for any breaches. And for the first time ever, they're using predator drones to watch the water patterns for any flooding."The Guard is also strategically placing one-ton "sandbombs" on cracks along levees and dikes. And, after a one-day break from sandbagging, volunteers have started up again. Peter Belleh and his daughter are on vacation from Texas and decided to help.Peter Belleh says, "It's not much of a vacation but I think this one in a million chance that you can volunteer and be part of a community."Officials say it could be several more days before the river drops significantly ... and two months of clean-up before they get back into the normal swing of things. Teri Okita, CBS News, Fargo.