We frequent a dog park/beach that is surrounded by water and our basenjis actually do go in the water now btw. Fiji will only get her feet wet - she used to jump backward when the waves came in. Bongo's basenji buddy Cairo will actually swim to chase a stick and Bongo is not far behind him. Go figure.
You may want to try frequently rewarding him for staying still before he gets a chance to complain. You can then start building up time between treats once he gets the idea that standing still will get him a reward.