recall at the beach

Question
I have 2 border collies,male5yo,female3yo.Both have very reliable recall,stay,down,etc.We take them on vacation with us every September to Hatteras, NC, as dogs are allowed on the beach(off lead) there after labor day.They are both pretty velcro, and are usually within 20 feet or so from me, but I find that with the waves crashing, and the breeze,I'm not loud enough for them to hear me and unable to whistle their usual come signal in the salt air. What visual signal(or something else) can I teach them for come?  I specifically want them to come to me and sit when I see a jogger or biker in the distance, and stay until they have passed.Neither dog is agressive in any way. Female is more wary of strangers and won't introduce herself, but male dog might, and I don't want to be another rude tourist.  Most of the time it's just us at the beach,but I'd like to be prepared, just in case!

Answer
Teach them an emergency recall using a real whistle.  I use the Acme Thunder, which seems to be loud enough for my dogs to hear at the beach.  To teach it, do this several times per day for a few weeks: Don't call the dog with the whistle to start with.  Simply get your dog's attention, blow the whistle and instantly hand him some chicken, roast beef, liverwurst, or cheese - something high value that he seldom gets, but loves.  Do this randomly from time to time.  Require nothing of the dog other than he just sits there, hears the whistle and is instantly given his special stuff.  After a few weeks, try blowing the whistle when he's in another room - of course, when he gets to you, have a roast beef party!!!  The beauty of this is that when the weather is good, you can use your regular recall - when the wind kicks up and you think your dog might not hear, just blow the whistle.  When he gets to you, he will forgive you the one time you only had biscuits for him because it was too messy to carry liverwurst in your pocket to the beach;-))