You can get a fairly thin, but strong, cotton rope from the hardware store for very little money. They have rope on big spools and you can cut off what you need. For a long line, you can cut about 30 ft...more or less. You can either tie it on the collar or buy (if you can afford it) a clasp to attach to the end.
As it was said, never punish in association with come. Punishment isn't always the obvious. People inadvertantly punish their dogs all the time when they call their dogs. For instance, they call them and the fun they were having ends. They come inside and the owner right away, leaves for hours. The dog comes and gets his nails clipped or gets a bath or some other equally unpleasant thing to the dog happens. Be sure that every time your dog comes to you, whether or not you called him, that it's the best thing ever.
If he just did something you don't like and then comes, again...never punish or scold him for that other thing. He will not want to come to you. If you have to go get him because he didn't come, don't punish. Anyhow, you get the idea.
Don't call the dog while he's engaged in something fascinating...while he's learning. You're setting him up to fail. Wait until he's already coming, until he's inches from you to use your cue. Take hold of his collar, give him a treat/praise, and then release him to go play again. If he's having fun, do this a few times before bringing him away from his fun. Then, once inside, continue some fun for a few minutes so he learns that coming does not equal the end of fun.
Never use your cue word with an angry, stern voice and don't use it to elicit the recall until he's reliable. Run the other way, squeek a toy, hide behind something and make a game. Just don't use your cue word if he's unlikely to come or you'll miss the association and he'll learn he doesn't have to come. And don't show him the treat first. In other words, don't bribe. Reward instead. Once he's coming regularly, you can use the cue word, but make it easy for him to comply. Start out with no distractions...or very few and increase distractions gradually.