Dom Littlewood goes behind the scenes at some of Britain's most secure institutions to see how they keep us and the country safe. Today, he sets sail with the Port of Dover police to see how they secure the country's border out in the English Channel. He finds out how sniffer dogs are trained and sees them in action, sweeping for explosives at London's ExCel centre. And home security expert Jenny Donaldson helps a single mum whose bike was stolen, by giving tips on how to secure her shed.