This verse amplifies the information about Zeniff’s guards: They are “spies. . . round about the land of Shemlon” who “guard” against the Lamanites. When the spies notice military preparations, they report their information so that the Zeniffites will not be caught by surprise.
The concept that the people would be “destroyed” by the Lamanite attack suggests a war of extermination. However, the Lamanites’ actual objective, achieved during Limhi’s reign, is subjugation. More likely, Zeniff sees his people’s political separateness, rather than his people themselves, as being destroyed. This is, in fact what happens: political dependency and heavy tribute. It is also possible that Zeniff is using “destroy” as hyperbole to incite the Zeniffites to greater military efforts.
Geography: The elevation of Lehi-Nephi and Shilom over Shemlon provided many excellent spying vantage points in Sorenson’s geographic correlation.