You mentioned you have 2.5 acres, so how wide is the border where the chickens are strolling over to your brother's place?? Deer netting is cheap, and although it's flimsy, it works well at keeping chickens in - you get 100 ft. length (6 ft. tall) for around $15. Sink posts (wooden or metal) every 10 ft. or so and run that stuff across the border.