Wullerton (spit) is the rival town of Dog River. The rivalry is so intense that whenever anyone in Dog River mentions the name 'Wullerton', they instinctively spit on the ground. Wullerton does not behave the same way. In the episode that Davis is forced to take a job as a cop in Wullerton (Gopher It), Davis tells his new partner that he used to work in Dog River and then spits. His new partner then says, "Why'd you do that?" - leading you to believe that Wullerton residents don't have the same rivalry with Dog River.
In the film, Wullerton is seen for the first time, as is the reason Dog Riverites hate it so much: Wullerton is a squeaky-clean, creepy, Stepford Wives-ish town where everyone is excessively nice and clean and helpful.