The easiest way to get your car back is to not let them take it in the first place. A repo man cannot enter a private residence to retrieve a vehicle. This does not extend to your driveway or a side street, but a man's garage is his castle. If you keep your car in a private garage, it will not be repossessed.
Just be aware that a trip to Wal-Mart, your work parking lot, or any other public space could give the repo man the window he needs for repossessions. They will watch your house, and they will follow you wherever you go. Be aware that, eventually, your repossession agent will come back with a court order and a deputy. Needless to say, at that point, hiding your car will no longer be an effective deterrent.