If you want to understand that issue, I suggest you read the Supreme Court's decisions involving religious monuments.
Such as...
Lemon v. Kurtzman, which produced the "Lemon Test" ?
• The statute must have a secular legislative purpose
• The principal or primary effect of the statute must not advance nor inhibit religion
• The statute must not result in an "excessive government entanglement" with religion
How about
Van Orden vs. Perry? Which says that a 10 Commandments monument is acceptable, depending on the context, because the Court chose to downplay or ignore the religious content, and classify it as a historical artifact and/or had a secular purpose? (In that case, the 10 Commandments monument was one of more than a dozen similar monuments, and nearly 2 dozen historical markers, relating to the history of Texas.)
Or perhaps
McCreary County v. ACLU of Kentucky, which barred multiple separate displays of the Ten Commandments, on the basis that those displays did not have a secular purpose?
Stone Vs Graham (10 Commandments displays violated Establishment Clause)
Lynch v. Donnelly (Nativity displays are OK because they have a secular purpose)
County of Allegheny v. American Civil Liberties Union (A nativity scene violated the Establishment Clause, because of how it was presented; a Menorah display did not, because of how it was presented)
Cuban Smokes' inquiry is valid. The answer to his question is, "it's allowed if you can convince a court that your religious display has a secular purpose, typically based on intent, context and other factors."
In this case, if Arkansas planted a 10 Commandments monument on a lawn, in isolation, with no prior notice, in the dead of night? I doubt it'd survive a court challenge.
Again, this does not justify vandalism. But it does answer Cuban's question.