Site send patrols every night, but the thief is still very hard to detect.

工地每天晚上都派人巡逻，但是小偷还是防不胜防。

youdao

What we're seeing are mats, patties, small concentrations, very hard to detect, but they're out there.

“也许‘浮油块’可能用词不当，”他补充道.“我们所看到油污的是护垫、小馅饼大小的，或者小的浓缩物，非常难以探测，但是它们就在那。”

youdao

Nighthawks were the world's first stealth fighters, planes that were very hard for radar to detect.

夜鹰是世界第一代隐形战斗机，很难被雷达发现。

youdao

Even if they are there, these B-modes will be very hard to detect, and the Planck team does not intend to make a statement on the issue until a further year of analysis has been completed.

BBC: The first fractions of a second after the Big Bang

Researchers at academic medical centers who study the disease say that so-called chronic Lyme, or post-Lyme, is very rare, hard to detect and not treatable with any further doses of antibiotics.

FORBES: Lyme Inc.