runaway dog

Seagull is a timid and nervous sheltie. I would categorise him as a difficult dog. He took 2 years to toilet train at home and his training comes along very slowly and every now and then he just lost all of them. I put these down to his nerves. Recently he tried to "runaway" again on the Common. He is a dog friendly dog and he loves to meet other dogs and most of the time he will walk away with the other dogs! The more you call him the more he will ignore you. I had enough of him running away and disobedient and was talking to people to find out what is the best thing to do with him, some suggested I should put him on the extension lead and train on the recall again and some said I should castrate him. Well, he is on the lead for more training for sure and I am not sure if castration will stop the running away?