KEY WEST — Two years ago Tom Dever finished first in the Half Shell 1/2 Marathon, leaving behind his competition in the seventh annual event.

On Sunday, Dever, 49, ran Half Shell again, finishing 23rd overall. But his goal was not to finish first this year. He wanted to run much slower.

Dever, along with training partner, Tim Fears, 41, entered Half Shell on Sunday as part of their training regime for a much harder race than the 13.1-mile course they both covered in 1 hour, 38 minutes and 37 seconds.

The duo is training for the Marathon des Sables, which is a six day, 151-mile endurance race across the Sahara Desert in Morocco. The event takes place at the end of March and the beginning of April.

Called the toughest race in the world, it equals the equivalent of five-and-one-half regular marathons.

In addition to the running, competitors are required to carry everything they will need for the duration of the run on their backs.

Mid-day temperatures run up to 120 degrees and the course unfolds on uneven rocky ground, with nearly one-quarter of their time spent running in sand dunes.

As a prelude to their longest day in the Marathon des Sables, Dever and Fears ran from Marathon to Key West with backpacks to help them get a little bit acclimated to the heat, although it was nothing like they will experience in the arid desert.

They also ran the Half Shell 1/2 Marathon with a five-pound backpack filled with a change of clothes for after the race.

"When we do the marathon, we'll carry food, water, clothes and our sleeping bag," Dever explained. "We will be carrying 15 to 18 pounds in the desert."

When asked why, Fears said, "Why not? It's a challenge. We've run Boston [Marathon]; we've run the Goofy Double at Disney last year so this is something different. We've run a bunch of marathons and Boston is the best, but this is the toughest."

"I love coming to Key West, this is one of my favorite races," Dever said. "Like Tim said, it gives us a chance to train in the heat. But the humidity over there is like only 10 to 15 percent."

Both racers are extremely excited about this challenge and look forward to more in the coming years.

"We're going to the Amazon in South America in 2008," Dever said. "Our ultimate goal is to run a marathon in every continent. I've done nine marathons but only in the U.S. Our adventures will start in Africa and then move on from there."