Your dog is digging, mouthing wet sand off a ball, and taking mouthfuls of sea between runs. Nothing looks wrong, and you are still not sure it is fine.
A beach is a lot of novelty for an adolescent dog. Most dogs swallow a little sand and a little salt water without anything coming of it. It is the amount that matters, and the amount you can control.
Why sand ends up inside your dog
Very little of it is deliberate. Sand comes in on a wet ball, off a stick, out of a hole your dog is digging, and off food dropped on the beach.
Leave the ball and the frisbee in the car. A wet toy dragged through sand is the single biggest source.
Feed and reward off the beach, or out of your hand rather than off the ground.
Interrupt long digging sessions by moving the walk along, rather than letting your dog work one hole for 20 minutes.
Rinse your dog's mouth and muzzle with fresh water if they have been mouthing wet sand.
Move away from any patch your dog has started to eat from, instead of correcting them for it.
Safety note
A dog who swallows a large amount of sand can develop a blockage, which is a veterinary emergency. Call your veterinarian if your dog is vomiting repeatedly, straining or unable to pass anything, or seems painful in the belly. The same goes for a dog who is hunched, dull or off their food after a beach trip. Say the dog may have eaten sand, because it changes what your veterinarian looks for. Do not wait overnight to see if it passes. A dog who eats sand persistently and deliberately is also worth a veterinary conversation, because eating non-food items can have a medical side.
Salt water and the drive home
A dog drinking sea water is usually thirsty, hot or enjoying the water. Drinking a lot of salt water commonly upsets a dog's stomach, and loose stools or vomiting a few hours later are the usual version.
Carry more fresh water than you think you need, and a bowl. A dog with a fresh option drinks far less sea.
Offer it every 10 or 15 minutes, before your dog goes looking for water themselves.
Keep the sessions short, and take breaks in the shade where the water is out of reach.
Skip the water retrieve. A dog carrying a ball through waves swallows sea water with every pickup.
Safety note
Call your veterinarian if your dog has drunk a lot of salt water and is vomiting repeatedly or has diarrhoea you cannot keep up with. The same goes for a dog who seems weak, wobbly, unusually thirsty, disoriented or unwell in any way. Too much salt can make a dog seriously ill. This is a phone call rather than something to manage at home.
After the beach
Rinse the coat, the belly and between the toes with fresh water.
Check the pads and the ears, and speak to your veterinarian about anything sore.
Offer fresh water at the car and again at home.
Give a smaller meal than usual that evening if your dog has swallowed sea water, and keep an eye on the next morning's stools.
Behaviour change is built from management plus reinforcement together. On a beach, almost all of the work is management, and there is no shame in that.
Today's version, in one line: toys stay in the car, fresh water offered every 15 minutes, and a rinse before you drive home.