Do you give your cat prescription CD (or is ot CDS?) food? I find as long as I keep feeding Cosmo (my cat) this stuff, he doesn't get urinary problems anymore. However, if I take him off the stuff for just a week, a vet trip is inevitable.
If you're not feeding it to your cat already, ask your vet about it. Cosmo had some serious problems a few years ago (he almost died twice because my family thought he could naturally "get over" it), but as long as he eats CD food once a day, he doesn't get those problems.