Post flags, hire lifeguards, who are you all kidding? No one would listen to either.
Our other home is at the Jersey Shore, near the boardwalk. The beaches are manned with lifeguards daily during the summer season, until 6 pm. Those who swim there do listen to the lifeguards - people do not swim at the sections where there are not guards - they're not allowed, and someone will come to escort them out with a toot of a whistle. The lifeguards undergo strenuous ocean training, and they include teenagers up to 'young' seniors who have lifeguarded their entire adult lives [many are teachers, some are firefighters, etc.]. They go out into the ocean several times a day, and if there are rip currents or undertow no one is allowed in those areas, or they are kept near shore. With all of that, every year there are drownings - almost always people who insist on going swimming after the lifeguards leave. Signs ignored. Signs would be even more useless here.
NOW - can you even imagine for a moment a Dominican lifeguard blowing a whistle and waving people out of the water, and someone actually obeying??? Forget the Dominicans. And the tourists wouldn't understand a word he was saying. Add to that the fact that unless someone has grown up near an ocean they might not even know such a thing as a rip current or undertow exists. They belong at the hotel pool.
That being said, plenty of Dominicans are very strong swimmers, I personally know more than a few of them, several who were lifeguards in their youth.