For myself I found the best way to teach a reliable recall is to play come chase me games. I adopted all of my dogs as adults, none had ever been trained or off lead or loose, it seemed to be quite a challenge but turned out to be very easy. With my Doberman I took him to a ball field which was fully enclosed and let him run around. I made sure I passed him a few times without trying to reach for him, just ignored him. Once he realized that I was just out for a stroll with him he wasn't anxious thinking I might put him on lead. Then I started running backwards and called him in an excited tone only once. When he came running to me I turned side ways so I wasn't facing him head on and played with him. I mention this only because you want to use unassertive body language when practicing recalls - it should be fun and non threatening.
I had a toy and started tossing it. This worked for all of my dogs, they learned that not every time I called them was an end to freedom. Some times when I call them its only to give them a treat, or to play catch etc. Dogs learn to avoid unpleasant events, this is why so many people have a problem with recalls.
The WORST things I have seen people do are: Calling the dog over and over and the dog learns to ignore the owner, owners getting mad and walking over and grabbing the dog and putting the dog on lead and then doing some recalls on lead - this really makes a dog want to avoid the person in the future
, think about what you can do to make you dog WANT to come to you, make it a good experience.
I always call my dogs in a happy tone, if they don't come right away I run away from them, this will trigger their chase motor pattern. I never run towards the dog or grab the dog. When they come to me and I want to put them on lead I make them sit and give a treat then put the lead on. Keep plenty of treats on hand and call your dog to you often when they are off lead and just give a treat. Make sure when your dog is busy sniffing a bush or object that you walk past the dog, this will give the dog confidence that every time you come up to them that you are not always going to capture them.
I also play hide and seek games with my dogs
if my dogs get too far ahead I hide in the bushes. When they come searching for me and find me I get excited and give plenty of praise when they find me. It is a game and I do this so my dogs always keep me in sight. I have 5 dogs and I have to have reliable recalls, I own 16 acres of land with many prey objects living here as well
All of my dogs love to come when I call them, they associate recalls with good things and praise. To teach a dog make it fun and upbeat, some people make the mistake of forcing their dogs to listen to them.
I have competed in obedience trials with my dogs for many years. People always got a kick out of watching my dogs do their recalls in the ring. My dogs just get so excited and exuberant.
Good luck to you.