τὸν πόλεμον εἰς ἅπαντα τὸν χρόνον κατασκευάζοντες.

This sentence is given anonymously in a list of translation exercises:
4 πάντα τὸν βίον ἐν κινδύνοις διατελοῦμεν ὄντες, ὥστε οἱ περὶ ἀσϕαλείας διαλεγόμενοι λελήθασιν αὑτοὺς τὸν πόλεμον εἰς ἅπαντα τὸν χρόνον κατασκευάζοντες.
Betts, Gavin; Henry, Alan. Complete Ancient Greek: A Comprehensive Guide to Reading and Understanding Ancient Greek, with Original Texts (Complete Language Courses) (p. 274). John Murray Press. Kindle Edition.

My intuition wants it to mean something like this:
We live our whole lives in constant danger, so that it escapes the attention of those who discuss peace that we must prepare for war all the time.
roughly = if you want peace, [you must] prepare for war.

The problem is that κατασκευάζοντες looks like "“are preparing” instead of “must prepare”.
Can anybody please throw in their two drachmas?

You’re understanding it correctly. Sometimes (not always) grammar trumps intuition.
“Our whole life we’re continuously among dangers, with the result that those talking about security have failed to recognize that they’re getting ready for perpetual war.”
It’s an inelegant adaptation of a sentence in a speech composed by Isocrates.

Thanks mwh!