Set up your cage in an area frequented by the possum you're trying to catch. Because possums are nocturnal, it's best to ready your cage just before sunset.
Tie the bait securely to one end of the nylon cord.
Place the bait inside the crate. Thread the free end of the cord through the slats or openings in the bottom of the crate and back inward through the slats so that the bait will hang from the slats when the crate is overturned.
Turn the crate upside down and position it on top of the board or plywood. Prop one edge of the crate on the forked end of the stick, keeping the stick as vertical as possible. The bottom of the stick should rest on the board.
Tie the free end of the cord about 1 inch above the bottom of the stick. Adjust the tension of your cord so that the bait hangs about 1 inch from the “ceiling” of the crate. The cage is now set.
Wait for the possum to take the bait. When the possum enters the cage in search of food, it will tug at the bait, pulling the string and dislodging the stick. The crate will fall closed, capturing the possum.