And so they should - he expects to wear through 15 pairs of them over the next two years, while heading east on a 29,000km round-the-world run.
The undertaking meant the 50-year-old was effectively running a marathon a day, for the next 700 days.
Mr Denniss began his bid at Sydney Opera House on Saturday, and has already made it as far as Ranfurly, in Otago.
Speaking to the Otago Daily Times yesterday, he said he aimed to become the first runner to circle the globe on foot while meeting Guinness World Record requirements.
That meant starting and finishing at the same point, running with an easterly component to his direction around the globe, and passing through opposing points - in this case, Wellington and Madrid - on either side of the globe.
Mr Denniss' run would take him from Sydney to New Zealand, then through North and South America, Europe and Asia, before crossing Australia again from the west to end where he began at Sydney Opera House.
He began with a short run to Bondi Beach on Sydney's coast on Saturday, before boarding a flight to Queenstown the next day, and since then has been plugging his way through Central Otago towards Dunedin.
He stopped in Ranfurly yesterday, aimed to make Middlemarch tonight, and arrive in Dunedin by Saturday.
"People could read it as a mid-life crisis ... I'm 50 now and if I left it too long I wouldn't be able to do it," he said.
He is being followed by his wife, Carmel, and a family friend acting as a support team, who help document his undertaking for regular updates on his website.
The aim was to raise at least $100,000 for Oxfam, and his reception in New Zealand had so far been positive. Some people had even offered cash as he ran; something that could lead to "heavy pockets".
He planned to run from Dunedin up the east coast through Christchurch, to the top of the South Island, then as far north in the North Island as possible, while maintaining an easterly aspect to his course.
The New Zealand leg was expected to take "six or seven weeks", after which he would fly to North America to continue his run.
He expected to pass through at least 20 countries and all continents except the Antarctic, while tackling the extremes of the equator and the Arctic Circle, the Andes and the Nullarbor desert, before arriving back in Sydney in late 2013.
"Assuming that I complete it, then I will be the world record holder for running around the world.
"I'm still not quite sure what I've got myself into.
"The first few days have been OK, but you do have hard times here and there, and when I do I wonder how I'm going to handle this for the next best part of two years."
Round-world run rules
• Start and finish at the same place.
• Maintain an easterly or westerly component in direction heading (no backtracking across longitudinal lines).
• Pass through two antipodal points (any two places exactly on opposite side of the Earth from each other).
• Cover 28,970km on foot.
• A total of 40,075km, the distance around the equator, must be covered; including travel across oceans by aeroplane and/or ship.
