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The two explosions at Monday’s Boston Marathon will lead to drastic changes in how large-scale public gatherings, particularly sporting events, will be secured, experts told FoxNews.com.

Mike DeCapua, director of Public Safety Consultants NW, said major changes to how law enforcement officials prepare for and respond to emergencies at events with thousands of participants, supporters or bystanders will “absolutely” occur following the two bombs near the finish line of Monday’s marathon, which killed at least three people and injured at least 176 others.

“That’s what’s going to happen,” DeCapua told FoxNews.com by phone while en route to large venues in Oregon where he would conduct security assessments and emergency planning. “When an event like this happens, you’re going to see more overt police presence and a lot more behind-the-scenes tactics that will make events like this much safer. And I think the public is going to be more vigilant, as well.”

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DeCapua — a retired Air Force lieutenant colonel and the former homeland security manager for King County Metro, Seattle’s public transit authority — declined to discuss specific measures that would likely be deployed for security concerns. But DeCapua said the largest challenge facing race organizers prior to Monday’s race was the enormity of the 26.2 mile course.

“One of the primary concerns is the size of the venue obviously, and we’ve done a lot of work in stadiums and that’s a fixed piece of ground,” he said. “But in this case, it’s impossible for an entire venue like that to be secured due to the sheer size.”

As a former bomb-sniffing dog handler, DeCapua said those animals have a finite amount of time regarding their olfactory senses to be effective in areas of high-concentration, particularly those with “nooks and crannies” along a lengthy route — as was the case in Monday’s bombing.

Another key challenge facing law enforcement officials is the diversity of competitors and their supporters at such international events, which makes profiling a virtual “nonstarter,” DeCapua said.

“Profiling in a crowd like that is next to impossible,” he said, adding that he would instead focus upon random searches, roving teams of investigators and hardened checkpoints.

With the London Marathon just days away, increased security measures can be expected at the race that drew roughly 37,500 athletes last year, as well as next month’s Kentucky Derby and Indianapolis 500. No known specific threats against the British race had been received, however.

Nick Bitel, the London Marathon’s chief executive, said security plans were discussed with police “as soon as we heard the news” about Boston and Indianapolis Motor Speedway spokesman Doug Boles said Monday’s incident will be considered when precautions for the race are considered.

“I guess this will bring a new topic or dialogue to those discussions, to see if there’s anything more we need to do to prepare with respect to what’s happened in Boston,” Boles told The Associated Press. “And we will learn more about that over the next couple of days, as the folks in Boston do, and we will be prepared for that.”

At the Kentucky Derby, which attracts nearly a quarter-million people at Churchill Downs Racetrack, security was heightened following the death of Usama bin Laden and officials there will be in “close and frequent” contact with local authorities moving forward.

“We are always in close contact at this time of year with the dozens of federal, state and local law enforcement and public safety partners who work with us every year on safety and security concerns for our major events,” Churchill Downs spokesman John Asher wrote The Associated Press in an email. “We will be in close and frequent contact with them and rely heavily on their expertise, as we always do, in the hours and days to come.”

Jessica Zuckerman, a homeland security analyst at the Heritage Foundation, told FoxNews.com she expects to see a “heightened awareness” at all large-scale public events in the near future and stressed the importance of planning ahead rather than responding to an emergency.

“The public will now be more aware of potential threats and one of the best things folks can take away from this is having an emergency plan with their families,” Zuckerman said. “It’s important to make sure you know where your loved ones are and how you’re going to react.”

Two sporting events in Boston -- Monday’s NHL matchup between the Bruins and the Ottawa Senators and Tuesday’s NBA game between the Celtics and the Indiana Pacers – have been postponed and cancelled, respectively. Elsewhere throughout the country, bomb-sniffing dogs were spotted sweeping the arena for an NHL game in Nashville and police officers were posted near the dugouts at the Padres-Dodgers baseball game in Los Angeles. Fans in New York to see the NBA’s Washington Wizards and Brooklyn Nets also met longer than usual waits at security checkpoints.

Henry Willis, director of the Rand Corporation’s Homeland Security and Defense Center, said the biggest challenge now facing officials at large venues is to understand where vulnerabilities exist during public events.

“Whenever you have a lot of people come together, that gathering is a potential target, unfortunately,” Willis told FoxNews.com. “You place more officers [at the event], you focus in with surveillance cameras, but there’s going to be limits, of course, to what you can do. That’s why preparing ahead of time really helps.”

The Associated Press contributed to this report.