Dave lives on a ranch, and has a mixed-breed dog named Chip.
Dave says as a pup, Chip would follow him through the orchards, always remaining close, and would come willingly when called. Now Chip is 10 months old, has discovered the joys of digging after gophers, and spends most of his orchard time running off, ignoring Dave's cues to come. Dave wonders what went wrong.
Simply put, Dave, when Chip was a puppy he felt more secure remaining close to you. As a rambunctious teenager, he is more interested in exploring the world around him, and has the confidence to do this on his own. This is a natural part of canine maturation. The trouble here is that Chip has discovered a high-level reward that he can easily get from the environment (the gophers), while hanging out close to you, so coming when called now is less rewarding.
Now you must back up a bit, and go through the steps to teach Chip a good recall. The key to a successful recall is convincing the dog it will always be worth its while to come to you when called, as it results in a high-value reward.
You know that Chip enjoys chasing gophers. What rewards can you offer him with more value? Come up with at least three top-level rewards. For example, try different treats. Perhaps Chip really likes bits of cheese or goes crazy for small pieces of chicken. Chicken would be the item to carry with you.
Does Chip play with toys? Does he enjoy chasing after a ball? What about a game of tug-of-war? Have a ball with you and/or a rope to play tug with Chip. Alternate at least three top-level items to reinforce coming when called.
You need to get a lot of repetitions. Begin with Chip on a short leash and call him to you when there are few distractions around - definitely no gophers - and reward him with one of the top three items. As his responses become stronger, faster and more reliable, practice around a few distractions and change to a longer lead.
Another effective technique is the Premack principle, or the relativity theory of reinforcement. Premack's principle suggests if a dog wants to perform an activity (chasing gophers in Chip's case), he will perform a less desirable activity (coming to you when called) to get at the more desirable activity. To accomplish this, have Chip on leash with you and when you both notice a gopher nearby, excitedly call him to you. When he gets to you, the reward you offer him is freedom to "go get the gopher!"
To have a really reliable recall, keep it "tuned up." Don't wait to call Chip when you need him to come; plan on making recall practice a part of your orchard routine, and call him 10 times on every outing. This will ensure Chip continues to get a high level reward for coming to you every time. It's that ingrained response that will result in him running right to you when you really need that recall to happen.