I need flea prevention on a budget...2 large dogs & 2 cats-Help!?

If you do not have a problem with fleas, I personally think Advantage is best - it is geared only towards fleas. If you go to your vet, get the biggest size they have. Your Great Dane & Shepherd will take a whole one, but you could dose it out for your cats (and probably have enough for 2 months from one tube). Ask your vet for the dosage!!