If you go down to the woods this month, be sure of a big surprise. Unless, of course, you are one of the 500-plus loons who have already signed up for the Deerstalker, an assault course through the countryside, forests and hills around the Borders village of Innerleithen.

‘I’d describe it as “fun run meets fell race meets Hellrunner meets tough guy’’,’ says Jim Mee, of organisers Detail, who introduced the Deerstalker’s city equivalent, the Rat Race Urban Adventure, to Edinburgh three years ago.

‘It’s fun, it’s fast, it’s action-packed and it’s as tough as you make it. It’s a rip-roaring tear across the hills, the bracken, and woods.’ Despite this hardcore description, he stresses that the Deerstalker event is not only aimed at lycra-clad fitness fanatics. ‘We’re hoping to create a really nice atmosphere; not just people putting on their trainers, going for a run and going home afterwards.’

The race begins at Traquair House in the Borders at 4pm on Sat 31 Mar. Runners can opt to take the 5km route, or the more challenging (and not for the faint-hearted) 10km course. After completing the first 5km of the course, those opting for more must put on a head torch and navigate the remaining 5km in the dark. Luckily you don’t have to rely on your own orienteering skills, as the course is mapped out from start to finish.

To liven things up further, participants are being encouraged to wear outlandish outfits, with the organisers themselves sporting tweed and Sherlock Holmes chic deerstalker caps. Mee says, ‘I think there’s going to be some pretty illegal lycra, lots of 80s-style headbands, and people in full deerstalker regalia.’ Whatever else you decide to wear, sensible footwear is advised.

Providing an incentive for participants to cross the finishing line, Traquair House will be serving up their own-brewed Deerstalker Ale to all those who manage to complete the course. There are also cash prizes for the winners and souvenir tankards for everyone who takes part. And if that’s still not enough, you can be hosed down by the fair maids of Traquair if you get really muddy. ‘It’s an optional extra,’ says Jim, grinning, ‘but I’m sure it will be very popular.’

Those who don’t like the sound of all of that exercise, or are worried that the only way they’d complete the course would be in an ambulance, can relax and enjoy the fair in the grounds of Traquair House, with food stalls selling local produce, archery and falconry displays and a beer tent. There will also be a camping village onsite so that people can travel from far and wide and make a weekend of it.

Anyone who wants to take part needs to enter soon. The event has been so heavily subscribed that it has already been extended to take 600 participants instead of the original 500. If demand continues at this level, further places may be added. After all, how often can you nip out for some rough and tumble in the forest, get hosed down, and watch some mud wrestling afterwards without risking arrest? Unsuspecting ramblers beware. The Deerstalker is muddily putting Scotland on the map as Europe’s adventure capital.

The Deerstalker, Traquair House, Sat 31 Mar, 10am-midnight, www.themightydeerstalker.com