Could you share with us the problems you've encountered adding chickens to your flock? Did you try to add adult chickens? That's the most difficult, by far.
Brooding day-olds right in the coop or run in full view of the existing flock, I find is the easiest way to get the flock to accept new members. The chicks are accepted by the flock because they are small and unthreatening, and by the time the chicks grow up, the flock knows them so well, there are rarely any problems.
I use the heating pad system, rig up a frame to form a warming cave right out in the run that's separate but in full view of the adults. When the chicks are three weeks old, I open portals into the rest of the run from the chick pen, allowing the chicks access to the entire run. By age five weeks, the chicks have been fully integrated into the flock and are moved into the coop to roost with the adults.
It's really the easiest way to add to your flock, as I see it.