Field techniques from the Vietnam War: Locating caches & scaring ducks

FP: The Best Defense, Tom Rick's Daily Take on National Security: Field techniques from the Vietnam War: Locating caches & scaring ducks
I'm always amazed at how refined field craft can become. Here are a couple of things that struck me in that essay by Col. Hoang Ngoc Lung, a former senior South Vietnamese intelligence officer, from Sorley's The Vietnam War: An Assessment by South Vietnam's Generals:

Floors, too, were good candidates for caches. The most effective way to detect them was to pour water over the dirt floor. Places that had been excavated would absorb more water at a faster rate than those that hadn't...

"The sapper threat was recognized and given high priority by security units. Small outposts took inexpensive measures for detecting infiltration which were nevertheless effective, such as raising dogs, geese and ducks on the outer perimeter of their positions...To deal with geese and ducks, they [the sappers] attached a stalk of blackened water potato plant to the end of a walking stick and dangled it upwind in front of the birds. Thinking they saw snakes, the birds did not dare make a sound. Another way they distracted the ducks and geese was to run green onion leaves on the sappers' bodies. The smell frightened the birds because they thought they smelled vipers." (pp. 118-119)