It can be a frustrating battle. After years of no fleas, I've been dealing with an infestation that came about as the result of a rat issue which has now been solved. I think I've got on top of it after about five months, but the problem is, flea eggs can lie dormant for three months plus, so the only solution is to treat and keep treating.
Ordinary frontline is marginal on effectiveness, but frontline plus still works well, as it renders any eggs sterile. Anything like Bob Martin is pretty well much quackery as it only repels fleas, it doesn't kill them.
Also, if you're flea-ing, don't forget to worm, as fleas are the intermediate hosts for tapeworm. That, of course, depends on the product, but some of the combination flea-worm products don't target all types of worms, so do check the small print on the packet.