For fascinating, low-impact aerobics, try deerstalking. I'm not talking about hunting but about searching out wild deer on their own ground and getting really, really close to them. It's a demanding sport but requires no equipment, just watchfulness and patience. Especially patience. And with the incredible proliferation of deer in virtually every city and suburb, you can go deerstalking just about anywhere.

There's no secret to the technique, which has been used by Native Americans since the dawnof time and is widely practiced by modern hunters, photographers, biologists and other wildlife watchers. It's a game of human wits versus the fine-tuned senses of one of the world's most alert animals. It can be played by anyone who can watch closely, step carefully and stand quietly. My son mastered it by age 6, and a family friend stalked deer well into his nineties.

If you're thinking this doesn't sound like much exercise, try it. Standing truly still for long periods requires such demanding muscle control that it regularly makes soldiers faint when standing in ranks. The aerobic part is the heart-pounding, breath-stopping, knee-quivering tension of trying to approach an animal whose whole being is attuned to maintaining awareness of everything around it and which at the faintest whiff of human scent or the sound of a snapped twig may explode into the spectacular tail-flashing flight that made "high-tailing it" part of the American language.

Another and better word for stalking is still hunting. Keeping still is at least half the game, because while deer can't tell unmoving humans from fence posts unless they hear or smell us, their eyes are acutely sensitive to movement. Scratch your nose or slap at a mosquito, and Odocoileus virginianus is outta there.

Hunters, myself included, tend to wear elaborate camouflage and use all sorts of cover scents and attractants designed to fool deer into thinking we're trees, bushes or hot-to-trot does. But we're just overgrown kids playing dress-up. Except for the floppy shoes, you could go into the woods costumed like Ronald McDonald and stalk deer just as effectively as some nimrod wearing $500 worth of RealTree camo and drenched in Doe Delight. I've had wild deer and wilder turkeys stroll within arm's length when I was dressed head to toe in blaze orange and looked like a Day-Glo popsicle. Deer can see some color, and can make out patterns, but it all means nothing to them without further clues of movement, sound or smell.

Smell is the deer's main and most effective defense. Humans continuously produce odors from every gland and orifice. Even those who bathe regularly and eschew scented products steam along trailing a comet's tail of pheromones, esters and miscellaneous outgassings. Fortunately for elevator users and subway riders, our noses are so lame that it normally takes a pitifully overperfumed person to reach our olfactory threshold. Unfortunately for deerstalkers, just a wisp of the cloud of molecules that envelops us is enough to shift deer into high gear. Whether you're an unwashed outlaw biker or Venus risen pearl-pure from the sea makes no difference; to deer all humans smell like the armpit of Hell. I've seen my scent spook deer that were hundreds of yards downwind. So upwind is the only way to go. Keep the wind in your face or fuggedaboudit.

The best place to walk up deer is a sizable, wooded public park, where they'll be more accustomed to people and so will tend simply to sidle away rather than flee if you spook them. Even if you startle a deer into full flight, don't give up; whitetails seldom scamper farther than the nearest patch of cover. They're curious creatures, and often circle back to check out intruders.

The ideal stalking ground is fairly open forest with rolling terrain and occasional clearings. Three of my favorites in this region are Rock Creek Park, Dickerson Wildlife Management Center in Montgomery County and Mason Neck National Wildlife Refuge with its adjoining local park near Fort Belvoir. All have gentle but varied topography and border the Potomac, where winds are fairly regular and predictable. And all offer plenty of "edge," the borders between field and forest that deer favor because weedy browse is abundant and escape cover is close.

Deer tend to work the outer edge, so I work the inner, using trees and brush to break up my outline. White-tailed deer seldom move along the high points of the ground because that "skylines" them, bringing them into sharp contrast with the sky or background. Follow their example. Avoid ridgelines, and travel sidehill, which generally gives longer sightlines. Best of all, follow deer trails, which are present wherever deer are. Deer are creatures of habit; they select the best routes through any terrain and stick to them. Many American thoroughfares follow what were originally deer trails that were adopted in succession by Native Americans, settlers and highway engineers.

So. Here we are in the woods on a crisp fall day, warmly dressed, comfortably shod and moving slowly upwind, looking for deer. Not looking for whole deer, mind. Unless a deer trots into view, what one normally sees is part of the animal: a twitching ear or tail or the horizontal line of the back against a backdrop of tree trunks. It takes time for the eye to sort out such fragmentary cues, so take plenty of time to scan the landscape before concluding no deer are present. Practice moving your eyes without moving your head and do everything in slow motion. Binoculars aren't much help, because what you gain in range of vision tends to be canceled out by the extra hand and arm movement. A good trick is to stand close to a tree, minimizing your outline. After a leisurely landscape scan, move to the next handy upwind tree.

In early fall deer are likely to be encountered in groups: bachelor bands of bucks and families of does and fawns, sometimes as many as four or five generations together. Later, during the rut, or mating season, the bucks shift from buddies to implacable rivals, and as the does come into season mothers drive off their offspring in preparation for serious sex. Before and after the rut, activity, i.e., eating, peaks at dawn, midday, dusk and midnight. In between, deer bed down and chew their cud, occasionally catnapping. They usually bed in fields or on open slopes, where their dirt-colored coats tend to render them invisible and the lack of cover makes us painfully obvious.

When the rut is on, which in this region is usually around mid-November, all rules are off. Bucks, normally super-shy, go dashing and crashing through the woods checking out every doe they see until they find one who's ready. Ready or not, she generally leads him a merry chase. If two fairly evenly matched bucks court the same doe, they lock horns -- antlers, actually -- and fight until one gives up and retreats (occasionally one or both of them dies).

There's a deer! Whoa. Power down. First, look beside and beyond the rascal to see whether it's alone. The more deer there are in a group, the more eyes there are to spot you. If you're lucky, the deer may be moving your way, in which case all you have to do is stand still and try not to sneeze. More likely, because they tend to move upwind, the deer may be moving at an angle to you, taking a few steps at a time as they graze and browse along. Move toward them when the deer have their heads down or are facing away. Be ready to freeze when a tail twitches, because that almost always means the deer is about to raise its head. Don't worry too much about leaves crunching underfoot; it's "white" noise that doesn't carry far. But stepping on twigs is tantamount to punching a fire alarm.

If you can move slooowly enough, you can actually advance on deer in an open field. I have watched a friend ease up on a group of five does and fawns over more than 100 yards of open meadow. He got within spitting distance of them before a swirl of wind betrayed him -- and then he was so close they didn't know what to do. Deer tend to become paralyzed in really close encounters, say within 25 feet. These stood there for a few long minutes, looking at my motionless friend, snorting and pawing the ground . . . and then went back to grazing. A deer's nervous system is so tightly wound that it cannot afford a long attention span; whitetails trapped in high-stress situations, such as a busy city street or a high-fenced yard, commonly die of nervous exhaustion.

Deerstalking is easier to describe than to do. My closest encounter with deer so far this fall has been about 50 yards, in three days of searching, with more than a dozen deer sighted. Several times I was betrayed by squirrels that scolded me and tipped off the deer. Once the stool pigeon was a blue jay. A flock of buttinsky crows followed me all over Rock Creek Park one afternoon, occasionally breaking off to harass owls or red-tailed hawks. More often I betrayed myself, by moving carelessly or impatiently.

But they were all good days, and great workouts.