A con game played with a chain, belt or string that is laid down to form two open loops. The mark places a finger or stick in one of the loops to try to secure the chain when it gets lifted, but the con artist is able to prevent this no matter which loop was chosen.
Characterized by caution; guarded; careful; on one's guard
Cautious of danger; carefully watching and guarding against deception, trickery, and dangers; suspiciously prudent
thrifty, provident