The mechanism that extends the arm, if powerful enough, whe reversed can lift the robot (1 motor, two functions) Once you latch the bar, you only have to lift a little to hang. I don't think a lot of teams will try to win by
messing with robots trying to hang. You want to score points, not try to prevent your opponents from scoring points.

A simple way to do this is a chain drive elevator using the door motor.



--- 2000 robot using chain elevator to lift scoring mechanism, hanging from bar.