Your wood trellis will last a long time in the garden, but you can expect that it will weather a bit. You may have to add additional nails over time to further strengthen the structure of the trellis. To prevent wood rot at the base of your trellis, hammer a steel rod into the soil with a mallet. Leave up to a foot of it above the surface. Lash the base of the trellis to the piece of steel. You can use any kind of thin wire for this purpose. The rods are available at the hardware store, usually in the garden area.