Las Vegas is getting set to host the first major event since the 1-October shooting.
The Rock and Roll Marathon and Half Marathon has 40,000 runners registered for Sunday's races.
As one of the rare events that shuts down the Las Vegas Strip, security concerns are heightened this year in light of the recent tragedy.
"Up until the shooting I honestly didn't even think about security as an issue and as soon as that happened, I was a little nervous," said Tom Sullivan, who will be running his first marathon.
Captain Andy Walsh with the Las Vegas Metropolitan Police Department is in charge of security this year.
He says marathon safety really changed after the Boston Marathon bombing in 2014, and 1-October changed it again.
"We've added some counter-sniper surveillance posts along the route," Walsh said. "We're going to have coverage from our helicopter unit."
He added there will be 350 officers on the ground plus several large vehicles like dump trucks and buses to act as makeshift barriers.
Some runners say crossing the finish line has become even more imperative now than ever.
"Just because this may be harder or scarier, it's not going to stop me," Sullivan said.
Esther Reincke is dedicating her run to Cameron Robinson, who died in October's shooting.
Robinson was her co-worker and running buddy.
"I can run now and Cameron can't," Reincke said. "That's really moving for me, to have somebody that was so young and so full of life and really just getting his life going."
Before the race Sunday, 58 white cross memorials will be moved from the 'Welcome to Las Vegas' sign to a museum.