Roughly half of the guns fuelling a gang war in British Columbia's Lower Mainland come from the United States, RCMP say, highlighting the difficult challenge of stopping the flow of weapons into Canada.

More than a dozen shootings in the past few weeks have sparked concern among the public, especially those living in the Metro Vancouver area. On Saturday, police in Surrey were investigating another two incidents that left one person wounded.

Last year, police confiscated 191 guns at the B.C.-Washington border. It's impossible to say how many others found their way into Canada.

"We know that they have been smuggled when we find them in the hands of criminals, being used in a drive-by shooting or a homicide," RCMP Sgt. Tim Shields told CTV News.

"But we have a very long border. In places, it's easy to smuggle contraband over."

At the Peace Arch crossing, roughly 4 million cars pass between Washington state and B.C. each year.

Police not only have to contend with the sheer number of vehicles, but also the sophisticated techniques used by smugglers to hide weapons.

Derek Collins, the chief of operations at the Port of Douglas, showed CTV News one secret compartment recently discovered in a luxury SUV. It was found by a dog trained to sniff out gun powder.

"The dog sitting down is an indicator some odour has been detected that he's been trained to find," said Collins.

When police removed a speaker in the trunk, they found extra wires with the ends exposed. They connected the wires to a power source, and motors whirred into action -- a panel opened, exposing a cache of handguns.

The owner of the vehicle was charged and banned -- at least temporarily -- from entering Canada.

Many smugglers escape charges, but Colins said that's changing.

"Our criminal investigations are increasingly laying more charges," he said.

"The sophistication of the concealment method, the intent, the purpose of the trip in Canada, the statements that were made prior to the discovery -- the type of weapon that it is. They all play into the decision to lay charges or not."

But Steve Fudge, president of the B.C. Crown Counsel Association, said gangsters and smugglers have other methods to avoid convictions.

"Tuck the gun under the passenger seat," said Fudge. "So the driver isn't in possession because he's not even sitting in the seat where the gun was found. And the passenger isn't in possession because his defence is, 'I just got in the car, I didn't know the gun was there.'"

With reports from CTV's Rob Brown and Shannon Paterson