This would be a useful feature. You can drag out a box, just like you do when making a stockpile, and your guard will only patrol in that area. You can set a different zone for each party.
I make 1x1 fallow fields at points I want patrolled. A banner or zone would be nice.
Great Idea^^ Was mentioned now sometimes 
until then: [A20+] Patrol Points
I think a connected point system wold be more handy. Where you plase ut point and then tell the grup to patrol in a clock or counter-clock direction from how you connected them up. This wold make it possible to have them go on nonlinear walls or on the perimeter
at start that is possible but later with crates not anymore (large creates etc, trigger also patrolling xD)