Very difficult to act in any way at all really without being branded a racist or a OTT bully. Speaking as someone whose club is a target for "thieves" taking fish for the pot i can say first hand that there is nothing much you can do save prey you catch someone in the act and then take an exacting and painfull revenge. Seems to me a cwt of lead and a big tarpaulin is the only real answer to these *******s.