Begin by getting your pup accustomed to coming to the whistle for a small treat. Condition this behavior to the point of habit, anytime, anywhere. Detach the check cord and replace it with a steady tab, a short lead about 8 inches long that can be used when necessary. Really, I don't ever have my pups at 4 months old off lead very often, only for airing, a short retrieve, and maybe to hunt a bit of cover for a tennis ball. Otherwise the pup is on lead with me all the time. Soon my pup realizes everything good occurs with me --affection, treat, a retrieve.