I have used Pet Protector to repel fleas from Boots for the last 8 years of his life.
I tried it because where we used to go fairly regularly had cats, and when we came home, Boots was carrying jumping passengers! I got him a Pet Protector. When we visited thereafter he always returned back home alone! When it stopped working he picked some more up from walking in the countryside. I replaced it and he doesn't pick any more fleas up. I reckon they work 99% of the time.
Although they are supposed to repel ticks too, in my opinion it works better on fleas.
They last 4 years and once you attach it to your dog/cat collar you don't have to worry about it.
No chemicals to contaminate your house or the environment at a time when the traditional defleaing chemicals seem not to be working so well and levels are rising in our waterways, which threatens our insect poulation, including bees that are very sensivitive to these types of chemicals. No risk of adverse reactions to the spot on products most people are encouraged to use on their pets these days. Adult healthy dogs are naturally immune to intestinal worms, and if you freeze your raw food before feeding then that kills any parasites in raw meat.
I can personally vouch for the magnetic field the Pet Protector emits because you can measure it, and I have done so.