Coordinate board, and lots of sentries. Something like this will suit your needs. Make it so if a player goes to a certain coordinate a sentry will follow right behind you. Depending on the size of your map, this might not be possible. If it’s a smaller map, this can work. But if you want to, I would just size it out really big, the zones, because a sentry will have lots of range, so there’s no need to make really tiny zones. I would do zones about 7-10 tiles large.
Hopefully this helps! And hopefully you will have enough patience lol.