Most fence stains provide a limited warranty when used on vertical surfaces—like fencing. These warranties are usually for four to six years, with some formulas extending the warranty to 10 years or more. This will give you an idea of how long your fence stain may last.  How often you’ll need to reapply fence stain largely depends on how much weather exposure the fence receives. Fences that are exposed to heavy precipitation and damp environments or those that receive direct, intense sun are likely to need staining more often. You might choose to reapply fence stain every few years to maintain the color and appearance of the boards. If you’re concerned with how well the fence stain is protecting the wood, a simple test can tell you if you need to reapply stain (or a sealer-only formula). To check the moisture barrier, sprinkle water on the boards. If the water beads up, your fence boards are still benefitting from your last application. If not, it’s time to reapply.