QUESTION:
How to repel sand fleas?

ANSWER:
Good question, and there are probably as many answers as there are cruisers. Here's our experience.

Mosquito Milk, by JABSCO. I've found it in St. Martin/St. Maarten in the Caribbean, and in Phuket, Thailand(! probably because there are so many European tourists there). It has a high concentration of DEET, and many's the time I was the only person not cursing the sand fleas. It comes in a roll-on bottle, looks a bit like deodorant.

Skin-So-Soft, by AVON. Many cruisers swear by this, though it didn't seem to work very well on me. I didn't like it too much because it was too oily for my taste.

If you get the sand fleas on the boat, I always had a 12V Vap-Mat to repel/kill them. I also carried mosquito coils ("FISH" brand), but I developed an allergy to the smoke, so couldn't burn them inside the boat, but did burn them in the cockpit, which did a good job of keeping mosquitoes and sand fleas away.

I don't know where you are cruising, but I noticed that a lot of cruisers bitten by sand fleas in French Polynesia developed infections and nasty scars. I don't know why the reaction was so bad, though it might be due to the fact that everybody keeps pigs - but that is only my theory. I suggest that if you get bitten by the sand fleas that you clean the skin with some vinegar - it's a very good disinfectant.

Fair winds,
Jeanne