Unless your deck is the plastic material (like TREX) it will require regular staining (and sanding). There are a variety of water-proofing treatments, some very expensive, that claim to do the job for 5 or more years. Since this is a nasty job, the longer the better.
Unfortunately, here in Colorado, I tried everything, regardless of price, and never got more than two seasons. It didn't matter if it was transparent, semitransparent or opaque (paint). Two years was the max. Failure to water proof the deck simply speeds up the decay and also makes the deck warp and splinter.
So, I repalced all of the wood with plastic. No maintenance now for 12 years and going strong. The plastic material does get a bit slippery when wet and hot when in direct sun, but the tradeoff for no maintenance seals the deal.
I would do (and did) the financial analysis comparing replacement with plastic against the biannual maintenance and ultimate replacement of the wood as it rots out. I was convinced.