As far as keeping track of free rangers, one thing you can do is train them to come when called by rewarding them with a coveted treat, such as scratch grains and/or birdseed. Use a distinctive call, one that they can easily distinguish from normal human talking (I yell chick-chick-chicken in a high pitched voice) and reward them everytime they come. Start by using that call whenever you give them a treat when they are in the yard or coop. After about 2 wks, they will associate the call with food and come running whenever you call.
However, if you are that attached to your chickens, I urge you to fence them in. You will eventually have trouble with predators, and if you keep free ranging, predators will eventually learn where the easy pickin's are, and before long decimate your flock. Many people keep on killing predator after predator so their birds can free range. Some of these predators are currently common, so people who kill them are not causing ecological damage, but as more and more people raise backyard livestock and control predators lethally, wild animal populations could decline to dangerously low levels. This did happen in the age of family farms in many parts of the US. So, (as a conservation biologist), I don't think lethal control of predators for backyard livestock is sustainable.
My chickens do not free range, but have a 1/3 acre fenced in yard. I can easily get them back into their coop in late afternoon, before many predators come looking for a meal, by calling and sprinkling a treat in the coop.