De Niro eat your heart out. Clooney take note. This is acting. My artfully crumpled body lies in the long grass; my face depicting the tragedy of a sad demise in the north Wales wilderness.

But my stellar performance as a corpse, or injured hiker (I like to keep my audience guessing), is more than amateur dramatics; it's also a healthy, sociable and community-minded British weekend away. By starring as a dogsbody – a volunteer victim waiting to be found in the great outdoors – I'm helping to train search and rescue dogs, and adding a new dimension to walking among Snowdonia's elegy-inducing peaks.

For me, a pet-less metropolitan flat-owner partial to the odd stroll with a pooch, the trip sounds promising. My mood lifts further with a drive along Glaslyn Valley, washed with a warm breeze and frescoed with rhododendrons. My target is Gelli Iago climbing hut, where 25 handlers, trainers and "bodies", and 15 dogs – collies, labradors and alsatians – are assembling, as they do every month.

While the rookie hounds remain below, I join Gareth Williams, an experienced Search and Rescue Dog Association (Sarda) handler who's running the higher altitude exercise. After a 30-minute uphill yomp – easy when you know the day's most arduous task involves lying still in soft grass – we establish HQ on a rocky outcrop. Hell, it's beautiful. To our right, cuddled by morning mist, lies Crib Goch, the Red Crag, while opposite is the immense south wall of Snowdon.

The training area sprawls before us like a vast natural flipchart: a square mile of verdant hillside, its border following a stone wall up to a crag, and crossing a saddle of land before chasing a rough track down to a stream. It hides three volunteer bodies: Pete, Elfyn and Ray. They could be the victims of a light plane crash, an avalanche or a four-wheel drive-by shooting.

As I rehearse my own "accident" (I'm torn between a shattered leg and hypothermia), Gareth, who like most handlers is also part of a mountain rescue team, explains the basics. It's all about the scent of a man. Or a woman. Depending on wind conditions, the scent (sorry if you're eating breakfast, but it's flecks of skin and bacteria carried on air vapour) of a person can be best detected in what is dubbed the "collective boundary". Today's light breeze has pushed it to the left-hand corner. The handlers – training is as much for them as the dogs – must keep their animal's cheek to the wind, zigzagging across the cone-shaped trail of scent and homing in on the injured or recently dead person.

The dogs clearly adore it. When handler Gaynor pulls on her fluorescent handler jacket, her nine-year-old collie, Pero, twitches with excitement. The switch is flicked. Within 15 minutes Pero has unearthed Pete behind a stone wall. Within 35, Elfyn is found underneath a wind-sculpted hawthorn tree, and, after ranging in and out of a final scent cone, there is Ray, tucked behind a crag.

It's enjoyable alfresco theatre; the silence of the mountains punctured by excited barking and Gaynor's praise at each find. Within 70 minutes all three bodies are in the bag, so to speak.

"It takes 30 or 40 people up to three hours to do a line search of a similar area," says Gareth. "A dog takes one hour. Night or day. In all weathers."

Now it's my turn. Mr DeMille, I'm ready for my close-up. My big break, literally, is to be an injured hiker – high on pain, low on Kendal Mint Cake – inside a sleeping bag, concealed by a patch of long grass above a tarn. After 10 minutes, sedated by clouds dancing across an impossibly blue sky, I doze off. My Oscar chances are fading.

Until. Suddenly. A rustle of grass. Fast canine breathing. Triumphant barking. I'm being licked. This is where an impetuous novice could ruin it. I don't move. Max shuttles back to Gareth, then me, then to Gareth, jumping for added impact. Thank heavens he isn't the rescue dog who had to be weaned off marking his discoveries with a shot of pee.

Only once the handler is with the body is it actually a find: mountain rescue will take over, and Max gets to tussle with his favourite tennis ball. "Amazing," says Gareth. "That's all he does it for. The play element is crucial."

My experience, to be fair, is merely a first taste, but if there are several dogs to train you could be out there for four or five hours – and, surprisingly, north Wales refuses to issue a warm sunshine guarantee. Later that day, as the last clouds disintegrate to reveal an epic horseshoe of peaks, I join Gareth and Max on a search for new bodies. It's easy to see why Sarda isn't keen on volunteers walking with handlers. The apparently smooth hillside morphs into ridges and rises, carpeted with thick grass, rocks and the occasional bog. The handler would need one eye on you as well as on the search.

It's also knackering, but allows me to chat to two of the bodies. "It's lovely lying out here on the hills, doing nothing," says Elfyn, a national park warden who has spent a decade as a dogsbody. "Look at the views. Is there a better way to spend a day?" As the labrador splashes in a nearby stream, the body sits up like a thirsty zombie, opens his flask and pours a cuppa.

Thirty minutes later, Max finds Ray. "It's not a normal hike," stresses the retired accountant. "You get less exercise. But it's incredibly peaceful and interesting watching the dogs. You feel proud when you hear of Sarda's successes. You feel a small part of it."

While bodying would be less jolly in a downpour or winter freeze – the conditions most people get lost in – the nights would still be enormous fun. Sarda Wales are a seriously hospitable bunch, although if you prefer soft sheets and top-notch cooking to hostel bunks and hearty stews, try Y Goeden Eirin, a homely, book-lined B&B near Caernarfon. Its slow-roasted lamb shank could revive many a body.

Next morning, down the valley, less experienced puppies are at an early stage of their three-year training. It's important work: 75% of Sarda's time involves lowland searches for confused pensioners or suicide risks. My second cameo of the weekend, as a hiker sheltering in disused farm buildings, ends after just 20 minutes, when I'm unearthed by a brilliant dog called Fly.

Two weeks later, I hear from Sarda Wales's chairman, Geraint Strello. An elderly lady was reported missing near the Menai Strait. After police helicopters and coastguards drew a blank, Sarda dogs found her in the early stages of hypothermia.

"Without our intervention this lady would have died," says Geraint. "If people didn't hide out for us at weekends, we couldn't perform like this. Every single participant in the training helped save her life."

• Sarda Wales' next training weekends (sardawales.org.uk) are on 13–14 August, 10–11 September and 15–16 October. Food and accommodation are free; you need boots and protective mountain clothing and must sign an indemnity form. Y Goeden Eirin (01286 830942, ygoedeneirin.co.uk) B&B costs from £40pp. Or try a two-person cottage at Bwthyn Samuel (01286 678626, bwthynsamuel.co.uk) from £60 a night