When you go to the trolley bay in the shop, you find that all the trolleys are locked together by chains. To release the chain you have to put a pound coin in a slot.
When you have unloaded your shopping into your car, you take your trolley to the return bays, slot the chain into the trolley in front and you get your pound coin back.
In our case, it would be a $2 coin. In the event that someone is too lazy to return their trolley, and take it home, there is a good chance that some youngsters will take it back to earn themselves two dollars.
It may not stop the taking of trolleys completely, but it would surely help to reduce the problem. Even if they just returned the trolleys in the car parks, it would minimise damage to vehicles due to wind blowing the trolleys around.