PCA does just that.
Did the Southern mainline presbyterian church have a similar rule when the PCA split from them?
Yes. While a split was already in the works, the deal had been that the southern churches would have an opportunity to leave if they didn't like how the merger was working (and a provision along those lines was eventually in the final merger documents as "Article XIII"). But at one point shortly before the merger, the exit clause was pulled out of the document, causing the initial exodus in a scramble to get out before the merger date. The liberals realized they'd overreached and backed off, but by then it was clear that they couldn't be trusted.