Every move increases the area needed to be blocked. Starting off, if the angel can move 1 every 1/9th of a turn, a devil could block off a 3x3. Every subsequen

Every move increases the area needed to be blocked. Starting off, if the angel can move 1 every 1/9th of a turn, a devil could block off a 3x3. Every subsequent full turn would add 2 that the devil would have to block off. So for move rate M on an NxN grid (which can represent any wandering linear path) necessary to trap an angel is 8+2NM (interestingly, close to 13). If an angel moves at all, the devil cannot trap it without player error.