well this is the problem with all monospace cars (SUV, Minivan, wagon, hatchback etc..) only solution is classic sedan and better something like my old Volvo 760/940 - it had rear seats with metal part behind them - no chance for anything from the trunk to get to the passenger area. Anyway my 850 has now the openable rear seats, so when I am carrying something extra heavy in the trunk I always buckle all three seats with the setabelts one cross another - it shall help in case of bad accident.