http://www.ehow.com/way_5632350_cat-...er-stones.html

Preventative Feeding
# Most veterinarians will recommend a diet for your cat based on human-grade meat, vegetables and fruits that is grain-free, and has reduced carbohydrates. A low-carb diet with higher protein creates acidic urine, which can help prevent the formation of struvite crystals.


Read more: Cat Food to Prevent Struvite Bladder Stones | eHow.com http://www.ehow.com/way_5632350_cat-...#ixzz158YSWM6g

And OMG - my Google search turned up this PT thread!
http://petoftheday.com/talk/showthread.php?t=151655