Marking drills need not be done in open fields or big stretches of open water. "Once a dog is using its eyes and marking well, it doesn't take any more than from two to six good marks a day, and the dog is back on it," Stewart says. "What you should be doing is more complex marks, like in woodlands. People do not spend enough time on that."
Stewart suggests tossing bumpers from fields into cover, or from cover into fields. "Get the dog tuned up to hunt the cover, to hunt the grass at the edge of water," he says. "Teach the dog to get into that cover, because if a duck is shot or wounded, it will usually head toward cover."
Do not forget marks that require the dog going over barriers. "I would do some marks across ditches, across fences and across water," Stewart says. "That's what the dog is going to have to deal with in the field."
The straighter the line a dog runs toward a mark, the less handling one is likely to have to do. "The object of these drills is to get the dog holding lines," Stewart says. "You have to put the straight edge back on them." Dogs will fade to the contour of the land, in accordance with the wind, or with natural barriers, such as ditches or other obstacles. "Teach them to run through the barriers," Stewart says. "You want the dog running a nice, clean straight line instead of scalloping."
One way to do this is to incorporate a natural or man-made straight line into the training. These can be as simple as a fencerow, or, in a more urban environment, a building. In either case, the longer the better. Place the dog in a sit position. Then toss a bumper parallel to the fence or building, either of which will then serve to discourage the dog from running wide. "The hardest thing to get a dog to do is run deep," Stewart says. "With the fence, you can teach the dog not to bow out. The dog should be running straight lines along the fence or building."
The time-tested baseball diamond setup remains one of Stewart's favored methods for fine tuning a dog's understanding of handling via hand signals and whistles.
With the trainer stationed at the imaginary "home plate," and the retriever positioned on the "pitcher’s mound," the dog can be taught to go right (toward first base) or left (toward third base) with overcasts, or toward second (with the "back" command) in search of hidden bumpers or bumpers tossed by hand.
One of the goals here is getting the dog to go after the bumper that you want it to retrieve first. The practical side of this is that during a real hunting situation, if two birds are on the water, one dead and one crippled, you likely will want your retriever to seek out the cripple first, to lessen that bird's chances of getting away. Handling can accomplish that.
On a somewhat related note, you will want the dog to make a clean delivery of the bumper or bird. Do not allow the dog to drop the object it is retrieving, or to play around with it. The bumper or bird should be brought directly to hand.