Well, there's a couple of things:
- when they're still young and less sure of themselves, take them into a field with fairly tall cover. Let them get out a ways and then lay down and hide. When they can't see you, they will panic a little bit and come back and look for you. After a couple of times of doing that, they will always want to keep you in sight, which will keep them closer. (This particular dog may be too old for that now.)
- make sure they understand and *completely* obey the "come" command. No matter what they're doing and or how interesting the smells are, they need to come to you whenever you call them. Whenever you feel like they're getting too far out, call them back and demand obedience. This might mean more time in the yard. Practice that obedience in lots of situations with lots of distractions (kids playing, cats running around, a tethered pigeon in front, etc.). Eventually, it will carry over to the field.
- when they're still young and less sure of themselves, take them into a field with fairly tall cover. Let them get out a ways and then lay down and hide. When they can't see you, they will panic a little bit and come back and look for you. After a couple of times of doing that, they will always want to keep you in sight, which will keep them closer. (This particular dog may be too old for that now.)
- make sure they understand and *completely* obey the "come" command. No matter what they're doing and or how interesting the smells are, they need to come to you whenever you call them. Whenever you feel like they're getting too far out, call them back and demand obedience. This might mean more time in the yard. Practice that obedience in lots of situations with lots of distractions (kids playing, cats running around, a tethered pigeon in front, etc.). Eventually, it will carry over to the field.