Louise I disagree with your trainer, if you never let him off how will he ever learn? Dogs learn by doing and they know you are the leader without all the mumbo jumbo that some trainers and behaviourists posion the air with. If they don't come back they simply don't want to because the distraction is more rewarding than the reward for coming back.

All my puppies have been walked off lead from the day they came home to me, all without any problems. If you keep him stuck on the lead he will see being off the lead as much more of a special treat and be even less inclined to come to you. If you only recall him when you really need him to return to you he will be much more inclined to return on your call.

Methical I never had a problem with other dogs coming over to him on the lead because they were usually too far away to want to come to him and also because the dogs around here are generally very well behaved and well trained.

Say it once and if she doesn't come either reel her in or just carry on and ignore her, don't keep repeating the command if it isn't being followed. When she does come to you repeat the command until she reaches you, this will drill what the command means into her, then reward the good behaviour and go from there.