Runners Lloyd Moreton and Phil Williams vowed "never again" after taking part in the world's toughest race.
The experienced runners, who have run several marathons, had so many blisters after running in the Marathon of the Sands across the Sahara Desert in Morocco they could hardly walk the final stages.
The blisters on Mr Williams's feet were so bad he has been on crutches since returning.
The two fathers from Rottingdean faced sun, sand storms, sunstroke, snakes and scorpions as they ran 147 miles in seven days in temperatures which ranged from near freezing at night to more than 100F.
At one point the temperature was 61C (150F) and another time they could only see three feet in front of them and had to crawl on their hands and knees during a sandstorm.
But Mr Moreton, 44, and Mr Williams, 40, kept on going and never thought of giving up.
They finished 406 and 407 out of the 750 started the gruelling run. Several did not finish.
Mr Moreton said: " You would think running on sand would be easy on your feet, but the Sahara is not all sand, you are running on flints and rocks for most of the time and they cut through trainers.
"The only people who were used to the terrain were the Moroccans and they just flew. The sweat on running shirts was so bad that when you took them off at night they literally stood up.
"It was an experience we shall never forget, but we will not do it again."
Mr Moreton will take part in the London Marathon on Sunday April 22 and then a fun run on April 28 round Hove Park.
They were running in aid of the Rocking Horse Appeal for the Royal Alexandra Hospital for Sick Children in Brighton, and are hoping to raise more than £5,000 for their endurance.
Mr Moreton will be running as a tree in the London Marathon to draw attention to the work of Partners in the Countryside, which helps to introduce more plants and trees into urban environments.
Mr Williams's feet are in such a bad state it is unlikely he will take part but he intends to take part in the fun run on April 28.
Mr Moreton said: "After taking part in the Marathon Des Sabres, the next two runs should be a doddle."
People who want to sponsor the runners should get in touch with the Rocking Horse Appeal on 01273 730286.
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