With my dog, Critter, the flags definitely helped him to know where the barrier was. Even living so far out in the country we had to get him a fence because he had started "herding" our neighbors cattle. He would run them in circles for hours. He's a mutt that we adopted from our local animal shelter. I'm guessing he has some type of herding breed in him. LOL. Unfortunately we had to go to a pet electric fence
with the wire instead of the collar because he figured out if he ran hard enough the little shock from the collar would send him over the barrier line. And he was off to chasing cattle. It is sometimes hard to put our pets in a situation that is nerve wracking for them, but with Critter and a neighbor threatening to shoot him we decided that his safety was much more important. Good luck and I hope everything goes well with the fence!