Secure border in record time — they’ll soon be gone (8)
I believe the answer is:
ephemera
'they'll soon be gone' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for ephemera that I've seen before include "Mayfly - something short-lived" , "They won't last long" , "of short span" , "Transitory things, lasting only a short time" , "Short-lived things of passing usefulness" .)