French police said they were trying to sniff out the kidnappers of seven highly skilled truffle-dogs which disappeared in southern France at the height of the season for gathering the pungent and costly black fungus. Three of the valuable dogs had since turned up wandering the countryside after the kidnappers apparently released them but four were still missing. Town mayor Herve de Chiree called a meeting of truffle gatherers and law enforcement authorities this week to discuss how to combat the problem but came up with few practical ideas, an aide said. Among possible remedies were rewards for the dogs` return or equipping other dogs with electronic tracking devices on their collars. Truffle-dogs are used to detect the delectable and highly marketable fungus in the region`s oak forests, where they grow buried in the ground. Years ago, pigs were used to hunt them out but dogs are now in favour, experts say. The police spokesman said they suspect truffle-hunters from a neighbouring area unwilling to put in the time and money required to train their own animals. A good truffle-dog requires a year or two of training and can cost up to 15,000 francs ($2,700). Truffles sell at the wholesale level for up to 1,600 francs per kg ($130 per lb).