Tampa, Florida -- The deadly shooting at the Naval yard in Washington D.C. leaves some asking how safe our military bases are.
"This is your fence line," says Mike Pheneger, a retired Colonel with the U.S. Army, as he outlined the northern perimeter of MacDill Air Force Base.
MacDill Air Force Base is a peninsula that Pheneger says has limited access points by car.
Securing the base has its challenges says the former director of Intelligence at US Special Operations Command at MacDill.
"You have this area here around the water that may be a problem." He adds, "On any large base people can get on a variety of ways."
In July, a homeless woman trespassed onto MacDill four times in three months -- twice by scaling the wall. In one of those instances, she scaled the wall by flipping over trash can and using it as a ladder.
Base officials stepped up security after September 11 at the vehicle entrances with pop-up barriers and armed military personnel. Once inside, Pheneger says there are layers of defense near sensitive buildings such as Central Command. And part of that defense is doing thorough security checks of people who have access to the base.
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"The dirty little secret," he says, "is it's very easy to get security level clearance. If your records are generally clean, then you'll probably get a security clearance check that probably will get you in the door."
In April 2010, Scott Bennett lied his way on base, lived there illegally and was eventually caught smuggling in weapons and ammunition.
Photo Gallery: Security breach at MacDill AFB
But security has worked in the past.
In May 2010, an FBI agent shot and killed a Vietnam Vet wielding a knife.
In June that same year, a couple was stopped at the gate and security found six guns, ammunition and military-style clothing in their car.
And in August 2011, base security stopped a former Army Ranger suffering from PTSD from bringing in a loaded handgun and 300 rounds of ammunition.
"The people at MacDill have taken all the reasonable prudent measures they can take and, even if they've taken those measures, still someone will get by. That's the dilemma you face," says Pheneger. "You can't have the perfect security system -- it doesn't exist."
Pheneger says all one can do is trust the system that is in place.
"You rely that the system screens out the bad guy but, every once in a while, someone will likely get through."
MacDill Air Force Base is a busy place. Officials say there are more than six million visitors each year, and while they do not typically discuss security measures in a statement, base officials say, "Our Security Forces go to great lengths to protect the people and assets assigned to the base."
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