Does Valspar have a cpating tha seals and stains that can be reapplied in a few years w/o having to take it down to bare wood?

If you are applying another coat of the Semi-Transparent Stain and the current coating has weathered sufficiently to allow new coating to penetrate into the wood then another coat of Semi-Transparent Stain can be applied. Otherwise the previous stain should be either sanded or stripped prior to applying additional Semi-Transparent Stain. If you are painting over the stain then the surface should be clean, dry and sound prior to applying the paint. We would recommend applying it to a test area first prior to applying it to the entire surface to ensure your satisfaction with the performance and appearance of the coating.