Here at the beaches of Da Nang there are a ton of rules. If you even come a little bit close to violating them the security will force you to stop. I get irritated about it at times because I just want to be able to get into the water where I feel like it.
But your post makes me believe that the lifeguards must know what they are doing and they patrol pretty darn closely here at the main beaches.
RE: You really should take the lifeguard swimming flags serious at Thailand beaches