The OK "state" Constitution does clearly define limitations of influence from religion.
https://www.washingtonpost.com/news...ic-display-of-ten-commandments-monument/No public money or property shall ever be appropriated, applied, donated, or used, directly or indirectly, for the use, benefit, or support of any sect, church, denomination, or system of religion, or for the use, benefit, or support of any priest, preacher, minister, or other religious teacher or dignitary, or sectarian institution as such.
And the Oklahoma Supreme Court held that the monument (paid for by private money, but installed on public land in 2012) violated that provision: