As gasoline prices continue rising in Iowa, so do reports of people filling their tanks and taking off without paying. Ron Marr, executive vice president of the Petroleum Marketers of Iowa, says more gas stations are having to take precautions against rip-offs. By posting someone with a clipboard to take down license plate numbers.Instead of posting someone with a clipboard in the lot to write down license plate numbers, Marr says other gas stations are simply requiring a 20-dollar deposit before allowing customers to pump their fuel. He says other security means may be better still.Marr says people who steal gasoline are making the bad situation worse as merchants have to pass on the costs of lost merchandise.Iowa gas prices are now 50-cents a gallon higher — or more — than they were at this time last year. One D-N-R forecast estimates prices could hit a dollar-80 a gallon in Iowa by summer.