Nope:
The majority of illegal drugs entering the United States enter in an assortment of vehicles, with drugs hidden in secret compartments in door panels or the roof, gas tanks, tires and even engines.
Cargo trains, tractor-trailers and passenger buses have been used to move illegal drugs. Trucks and trains carrying fresh produce such as watermelons, limes and other fruits bring in millions of pounds of illegal drugs.
The next most common method of bringing drugs into the US is cargo ships and planes.
The least likely method for bring drug enter into the US is individuals carrying them across the border. One semi properly outfitted can bring in more drugs than 50 backpackers. One ship cargo container can bring in more drugs than a 700 backpackers. It's a matter of economic. Meeting the demand for drugs in the US with back packers coming across the border would be both impossible and far more expense than other methods. This is why building walls or other barriers along the border would have very little impact on drug importation.
The profit margin on illegal drugs is so high, you could close the entire southern border and all it would do is raise the price of drugs to cover the added cost of alternative transportation.
By Land, Sea or Catapult: How Smugglers Get Drugs Across the Border